In late December 2003, a massive earthquake levelled the ancient Iranian city of Bam. More than 30,000 people were killed, and about 100,000 others were left homeless. The quake also destroyed the city's 2,000-year-old citadel, the world's largest clay structure. We look at the massive international aid effort to dig out the dead and keep the survivors alive. We'll also look at whether such a tragedy could happen here.