country. >> to protect the city from flooding, levees have been built there since the 1700s, but as the city expanded, it became more vulnerable. catastrophe struck in 1965 when hurricane betsy, a category 3 storm at the time of impact, caused the levees to fail. the whole city flooded, just like during hurricane katrina. after betsy, the u.s. army corps of engineers redesigned and rebuilt the levees around new orleans into a system thought to be strong enough to hold up against the same strength storm, a category 3. >> we now expect katrina's hurricane force winds to reach the louisiana coastline as early as this evening in new orleans before sunrise. >> when hurricane katrina grew into a category 5 with a bull's eye on the city, then mayor ray nagin ordered a mandatory evacuation. >> this is very serious, and it's of the highest nature. >> those who could not get out, were told to go to the superdome. >> at noon today, the superdome will then be opened up as a refuge of last resort. >> this is the superdome, where tonight a crowd of 20,000 to 30,000 people expected. i was among the thousands inside