known, dies. >> with constantine and helena, what we're seeing is christianity moving out of the shadows into the mainstream, but now into the dominant position. it's not just a religion. it's the religion. now the roman empire's going to be christian. the known world's going to be christian. >> but the question remains, did helena actually discover the cross jesus was crucified on? at the oxford university radiocarbon accelerator lab, archaeologist dr. georges kazan and professor tom higham are about to take a step closer to solving this mystery. by carbon dating a fragment of the true cross given to the king of ireland by the pope. in 1100 a.d.