then a roman empress, helena, sets off on a dramatic quest to find it. >> helena changed everything. the discovery of the cross is shrouded in mystery. there's intrigue. there's murder. there's sex. there's violence behind all of this. >> her discovery will be hacked into tiny pieces and traded around the globe, venerated by millions, ridiculed by others. >> i don't think there's a snowball's chance in hell that helena discovered the true cross. now for the first time, modern science set outs to answer the question: is the true cross a hoax that mocks the crucifixion or the relic of relics? >> the true cross is one of the greatest mysteries of christian history. we have the tools to solve it. >> the cross, an object of savage torture. >> that cross was an instrument of death, pieces of wood nailed together to kill a human being. >> but also an object of deepest veneration. >> the cross on which jesus died really symbolizes for me the greatest act of love in human history. >> the cross remains hugely powerful because jesus survives the cross. he doesn't just die an ignominious, shameful death, but rises to new life. >> the cross is now the ultimate symbol of christianity, adorning vast cathedrals and houses of worship the world over, but in some churches, they have crosses said to be made out of the actual wood jesus died on, the true cross. >> the true cross is surely the most important object in christian history. >> to touch a piece of the true cross is the opportunity to reach across time and space and human history and grasp something that changed the world. >> to the churches that hold them, fragments of the true cross are a miraculous link to the son of god, but could these relics possibly be real, and where do they come from? according to church tradition, 300 years after the execution of jesus of nazareth, the mother of the roman emperor constantine, empress helena, arrives in jerusalem. >> she is arguably one of the most revered women of antiquity and of all time. >> she has come to lead a dramatic excavation on the site of christ's crucifixion. >> she has been called the first archaeologist. she is said to have personally discovered the most sacred symbol in christianity, the true cross, the cross on which jesus was crucified. >> the story of helena puts her at the heart of the story of the christian faith. >> helena is said to have broken up the cross and sent it throughout the roman empire, but as the legend grew, so did the number of relics. there are now more than a thousand scattered around the world. >> they're in trinkets. they're in necklace amulets. they're embedded underneath altars, and so there is a good bit of skepticism about relics such as these. >> one of the first people to publicly question the authenticity of the true cross was the 16th century protestant reformer john calvin. >> he says, "you can't walk into a church anywhere without seeing a piece of what's supposedly the true cross." >> calvin laughs and says, "you know, if you took all of the pieces of the true cross and put them together, they would fill a ship." >> and yet scripture says that just one man, jesus, was able to carry it on his shoulders. >> there were a lot of people who were speaking out about the devotion of relics as something which is absurd and disgusting, and they really thought that people had lost touch with the true faith. >> the true cross had the power to divide christianity, and the question remained: could the legend be real? high in the cantabrian mountains of northern spain lies the monastery of santo toribio de liebana. it's home to the largest and most revered piece of helena's discovery. dr. georges kazan is an archaeologist here to investigate the mystery of the true cross. >> what's at stake here is the truth about the origins of this relic. is it something that dates back from the time of christ? >> this relic is said to have been brought in the 5th century from jerusalem by a monk called toribio, and this relic is enormous by the standards of relics of the cross. there's not many relics that are anything like this size. there's a little window here where you can actually touch the wood itself. unfortunately, we can't open up this reliquary and take this wood with us or subject it to any scientific sampling. however, what i'd really like to do is to get something like it into a proper laboratory environment where we can explore it further. >> to help him in his search, dr. kazan's starting point is a fascinating project by a 19th century french architect named charles rohault de fleury. he set out to add up all the pieces of the true cross. >> this map shows the places which he documented as having wood of the cross, and he worked out that all of this wood from all the places that he'd been to didn't come up to 10 percent of the total volume needed to put up a cross of the size required to crucify christ. if rohault de fleury is right, calvin must be wrong. >> now kazan will use de fleury's map to help locate relics that his team can then carbon-date. >> we would want to find relics, subjecting these to scientific analysis just to see how much of the legend might be true. >> man: what's my safelite story? 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(gasps) ♪ did it work? only pay for what you need ♪ liberty. liberty. liberty. liberty. ♪ spider-man no way home in theaters december 17th according to church history, 300 years after the crucifixion of jesus christ, the most important woman in the roman empire, the empress helena, sets off on an epic quest to find the actual cross jesus died on. >> when helena herself went to the holy land, nobody's ever done this before. >> she is likely to have left from rome. to reach jerusalem is almost 2,000 miles over land. >> for an elderly lady -- helena was in her 70s at this point -- this journey is an enormous undertaking. >> it is so unbelievably far away. in the american context, if new york is rome, jerusalem is something like guam or american samoa. >> but by all accounts, helena is a remarkable woman. we know only a couple of things about the empress helena. we know that she was christian, and we know that she was a commoner. >> and yet she gets together with a traveling roman army officer and gives birth to the man who will one day become emperor of rome. >> since its creation in 27 bc, the roman empire has been ruled by pagans. then in 312 ad, helena's son, constantine, has a dramatic change of faith. >> the story goes that on the eve of a great battle outside rome, he has a vision. >> he sees a cross of light in the sky, and he hears a voice that tells him, "by this, you will conquer." he takes it to mean that by the symbol of the cross and by christianity, he's going to become the lone emperor and the supreme figure in the known world. >> he wins the battle and becomes the first christian emperor. >> christianity is very much a minority cult practiced probably by no more than about 10 percent of the empire's population, if that. >> it's almost impossible to underestimate the impact of constantine's conversion to christianity. before that, the empire had been persecuting its christians. >> it was illegal by the penalty of death to be a christian. after that, you were free. >> constantine legalizes christianity throughout the empire. fourteen years later, his mother is on her way to the holy land. >> i think that she was sent by the emperor constantine. he felt that the cross was very important, and he wanted to send her there to do something special. >> there is potentially a darker side to helena's journey. it follows on from a scandalous episode within the house of constantine. >> constantine abandoned his first wife to marry the noble woman fausta. fausta has given him three young sons, but her husband's likely successor is his eldest son, crispus. crispus was the golden boy of the constantinian household. he'd had a very successful military career. he'd been made caesar by his father. >> on the face of it, the christian family at the center of the roman empire are united, but a scandal is about to erupt. >> christian sources tend to hush-hush about it. they don't wanna say anything, but the pagan sources jump all over constantine. the story goes that constantine discovers that his son, crispus, his favorite son, has been having an affair with constantine's second wife, fausta. >> what we're told by the sources we have is that on the orders from his father, he is sent to a place called pola on the coast of croatia, and he is put to death by poison. >> helena was crushed by this scandal. this was likely her favorite grandson. >> this must have been devastating for her. >> but the scandal is about to get bigger. >> constantine discovers from back channels that perhaps fausta had manufactured all of this, that she favored her own sons for the throne and that she set crispus up to be murdered. he orders that she be put in a bath chamber, the doors locked and the fire stoked up to the point that it cooks her to death. >> as the self-proclaimed christian emperor, he's engaged in the sin of murder. thou shalt not kill is one of the top commandments. constantine will have thought of helena as his great ally, thinking that he can rely on his mother's support in anything. perhaps he should have thought again before he killed her grandson. >> you are weak. you are a weak and sinful man. >> the murder of fausta and of crispus happens in 326. helena departs for the holy land in 327. there's almost certainly some connection between those two events. >> if you're his mother hoping for his soul to be saved somehow, you're going to want to make a passionate gesture of reconciliation, of penitence. >> she knew what she wanted when she traveled to jerusalem, and when she went looking for that true cross, she was surely determined to find it. >> man: what's my safelite story? 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well, it really takes us back to the year 135 ad when the emperor hadrian built a pagan temple over the site, and it ends up marking for all of posterity the place of his death. >> the year before, helena's son, the emperor constantine, ordered the temple be torn down. >> it wasn't his policy to destroy all of them, but that temple was the very antithesis of what christians thought christ was about. >> the account of what happened next is recorded in a later church history. >> at some point, perhaps as easy as the 360s, we begin to see a legend emerge that describes helena's role in the finding of the true cross. >> we're told that helena personally, with her own bare hands, removed some of the earth and uncovers three wooden crosses jumbled together. >> but when she came across what she thought was that relic, one can only imagine the emotions that welled up inside of her. >> the reality is that we don't know precisely what happened in jerusalem, and my own personal belief is that helena found something that she believed to be the true cross. right, girl? >> singers: ♪ safelite repair, safelite replace. ♪ feel stuck with student loan debt? move to sofi and feel what it's like to get your money right. ♪ ♪ move your student loan debt to sofi— you could save with low rates and no fees. earn a $1,000 bonus when you refi— and get your money right. ♪ according to christian history, 300 years after the crucifixion of christ, helena, the empress of rome, discovers the actual cross jesus died on. >> from the moment that the cross is found, people become interested in having a piece of the wood itself because of its direct connection to the body of christ. >> legend says helena divides the cross into pieces. >> i imagine when helena broke up the cross, it was such a desire for her to take it with her, to be able to share this tangible representation of her savior, of her lord. >> sometime later, pieces of the true cross start appearing throughout the roman empire. >> our first evidence that fragments of the cross are being spread around the mediterranean is from the late 340s and 350s when we learn that people have taken pieces of the true cross over to the north african seaboard. >> if the helena tradition is correct, then that would only have been 20 years or so since its first finding that shows that physical particles of the true cross actually did spread out from jerusalem very, very early on. >> there must have been the discovery of the wood by helena or someone for this trade in relics to have really boomed. >> this really becomes a new moment for christianity in which the cross becomes something that they are no longer afraid to talk about or to signify. >> before, the cross is basically a symbol of defeat, a symbol of humiliation, a symbol of death. people were familiar with the horrors of roman crucifixion. >> the cross is an instrument of capital punishment, and it's quite amazing. it's one of the big stories of early christianity that the instrument of the execution and torture of jesus christ over time becomes the primary symbol of jesus christ. >> one of the key factors in the change is helena's pilgrimage to find the true cross. it changes the cross to something that actually becomes something tangible that people want to think about as part of their devotion. >> as fragments spread around the world, they will also help turn christianity from an underground cult into a global religion. >> pieces of the true cross were almost used like trading cards. this is a way to gain favor with a bishop here or an aristocrat or prince over there. >> if you shared the true cross with someone, you're sharing power with them because the true cross is a source of religious power. people are going to respect you for having a piece of this. >> the legend of helena's discovery would change the course of christian history, but could what she found have been the actual cross jesus died on? now the modern-day investigation into the true cross is gathering pace. the city of waterford is the oldest city in ireland. it boasts a long history of christianity and a museum that holds an important relic of the true cross. >> what's fascinating is that it is said to have been given directly by the pope to the king of ireland, and rome, as we know, had access to relics from jerusalem. >> archaeologist georges kazan is joined by scientist tom higham. he is also from oxford university in england, and he will put the relic to the test. >> for the first time in history, we're able to place these relics in their proper time and proper date. >> the waterford cross is on loan to the medieval museum from the roman catholic archdiocese, and museum curator eamonn mceneaney has secured their permission to test it. >> and the relic is just inside this? >> it's just inside this. >> is that a modern script or an ancient script? >> no, it's a 12th century script. it says, "a piece of the wood of the true cross, and it was given to the king of muenster by the pope 1110." >> so we can date it at least back to 1110. the cross is believed to be cedarwood, and since its arrival in ireland, it has been carved up further to share with different churches. >> you can see it quite plainly here on the back. >> ah, ah wow. >> again, you can see a sample was taken from here. >> what kind of information do you have to say that this cross may have come from jerusalem? >> well, to my knowledge, cedarwood certainly wasn't available in ireland in the 12th century. it would have to come from the middle east somewhere, lebanon or israel. >> but could this piece of wood come from 1st-century jerusalem? the time has come to find out. 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ask your health care provider today about once-weekly ozempic®. oh, oh, oh, ozempic®! you may pay as little as $25 for a 3-month prescription. are you a christian author with a book that you're ready to share with the world? get published now, call for your free publisher kit today! this museum in waterford, ireland, claims to hold a piece of the actual cross that crucified jesus, the true cross, a relic said to have been discovered by the empress helena 300 years after christ's death. eight hundred years after that, the pope would give this piece of it to the king of ireland. when the pope gives you a relic of the true cross, he's almost saying, you know, "you're a real king. you've got that legitimacy. you've got that power." >> for the first time in history, a prized relic of the true cross will be carbon-dated. professor tom higham has over 20 years experience. >> there's quite a lot of what looks like lacquer that's across the top of the wood, and lacquer will have a different radiocarbon concentration, probably to the age of the wood, but fortunately, pieces of material have been taken, and that exposes the actual wood, so that's a good place for us to take the sample from. >> the procedure should leave little perceptible trace of damage in theory, but it's a nerve-racking business. >> i'm just gonna take a small bit from here. >> yes, tom, as small as possible, a very, very small piece. >> we only need about 10 milligrams. >> that's equivalent to a few grains of salt, but this relic has been venerated here for almost 1,000 years. every speck counts. >> it's very, very hard, this wood. >> could that mean anything to do with its age? >> possibly. i mean, it looks -- it actually looks old, this wood. but it's just, you know, it looks aged. so far, so good. >> tom is satisfied with his sample. now they can head back to the lab to test for the first time this piece of the true cross. eight centuries before the waterford cross arrived in ireland, helena will continue her tour of the holy land, and with the backing of her son, the emperor constantine, she will transform the landscape. she builds churches on the site of christ's birth in bethlehem and one to commemorate his last moment on earth. >> constantine made it legal to practice christianity. helena gave christians places to practice christianity. before her arrival, there were no christian buildings in this land. christians met here on the mount of olives to commemorate jesus' ascension, but they met secretly, we're told, in caves. after helena, a structure is built on this site, and christians can come here publicly and openly to remember this important part of their faith. >> for a religion that had been illegal for over 200 years, it's a defining moment. >> she makes the holy land holy, and the churches that she built are ways of literally cementing in the ground christianity in the holy land. >> it reinstates it as the place where people want to go and remember jesus' passion. >> arguably, helena and constantine's biggest contribution to jerusalem is the church of the holy sepulchre, said to be built on the site they believed was golgotha, the place where jesus was executed, but did they get the location right? >> based on the archaeological evidence, this would be a logical place. it was just outside the city walls, and romans liked that for crucifixion, so right now, there's no better candidate than right here. >> the church has been rebuilt several times, but its core goes back to the 4th century. >> we are deep, deep inside the lowest level of the church of the holy sepulchre, and this is the place where tradition says helena found the true cross. >> after her tour of the holy land, helena begins the long journey home, but did she do so, as legend says, with a piece of the cross jesus died on? dr. georges kazan heads into the lab to carbon-date for the first time a relic of the true cross to find out once and for all. ♪ limu emu... & doug ♪ ♪ superpowers from a spider bite? i could use some help showing the world how liberty mutual customizes their car insurance so they only pay for what they need. (gasps) ♪ did it work? only pay for what you need ♪ liberty. liberty. liberty. liberty. ♪ spider-man no way home in theaters december 17th mom, hurry! our show's gonna start soon! i promised i wouldn't miss the show and mommy always keeps her promises. oh, no! seriously? hmm! it's not the same if she's not here. oh. -what the. oh my goodness! i don't suppose you can sing, can you? ♪ the snow's comin' down ♪ -mommy? ♪ i'm watching it fall ♪ watch the full story at www.xfinity.com/sing2 she returns to rome to find the pilgrimage. her triumph will be short lived. >> helena dies shortly after returning from heidi land. >> it's incredible to think about the power of this one woman's spiritual drive and the impact that it had on history. her influence upon her son constantine will change the faith of the empire and the fate of christianity. a decade after her death, her son falls ill. he takes the final step and asks to be babbtptized. >> there were so much of c con constantine's life that didn't line up. >> i think he had a full c conv conversion. constantine the great dies. with them, now into the dominant position, it's not just a religion, it's the religion. now they're going to be christians. the known world is going to be christian. but the question remains did helen discover the cross jesus was crucified? archaeologist and professor tom are about to take a step closer to solving this mystery. >> the true cross is the most important relic. to have it tested in this way could reveal the story potentially true is fascinating. >> this is the first time we actually have direct data of the true cross. >> it involves a series of stages. first of which is to preclean and pretreat the samples and remove any thing that ultimately results -- >> the final stage of the process, enables us to measure particles of carbon 14. the less radio carbon -- we can date anything from the present day back to about 50,000 years ago. >> inless than 20 minutes, they may solve an enigma that dates back 2000 years. >> could the waterford cross be part of the cross helena said to discover? >> let's have a look and see what rulss in it. we can see it here. >> this relic of the truth cross dates from 1100 a.d. >> that's not the age of the true cross. >> okay. >> maybe around 1100? >> it's not the date they were hoping for. it does reveal the relic's rich history. it's very interesting because it seems to match in with the date of the script on the back of the relic. this is a time when the cross is similar and the relic were exceptionally important for the spread of christianity so the fact that this relic was created around that time goes to support how important that was. >> for hundreds of year, the true cross continues to play a central role in the story of christianity. and though this relic is only a thousand years old. others may prove far older. >> this is the first step of a long journey to investigate morrel more relics of this type. at the church of the holy accept of jerusalem, they continue to separate. in a church she built, in a city she reclaimed. >> helena is the person who takes jerusalem and turns it into this place that we are all looking to for a spiritual message. >> for centuries, devoted pilgrims have come here to mark their faith with a symbol that's recognized the world over. >> at the time of jesus, across was a negative image. it was a place of brutal, horrible executions and deaths. but after helen and constantine, the cross becomes a symbol of salvation. without the story of tp discovery of the true cross, helena would be just another empress. but, this story plays the heart of the christian faith. she gives christianity a symbol. without her, christianity would not be the religion that is. john the baptist. the fearless prophet, he believes that some reckoning is beneath. the preacher that baptize jesus, setsi setting him on his mission towards god. >> now f science joins the quest to connect past. test the relics to discover the link to a man that the bible says was john'