In pictures: Bam before and after

1 of 7 The historic citadel at Bam was one of the treasures of Iran, dating back to pre-Islamic times.

2 of 7 It was built entirely of mud bricks, clay, straw and trunks of palm trees - it was the largest adobe structure in the world.

3 of 7 The city was used as army barracks until 1932 and then abandoned, but work began on restoring it in 1953.

4 of 7 It attracted thousands of tourists each year.

5 of 7 But Friday's devastating earthquake has virtually levelled the historic heart of Bam.

6 of 7 A composite of pictures taken after the earthquake and, below, in 1975 from the same vantage point.

7 of 7 The United Nations' cultural agency, Unesco, has asked for permission to send experts to assess the damage.