BBC - MYTHS AND HEROES: THE QUEEN OF SHEBA: The Great Dam at Marib, Yemen

Completed in the 8th century BC, this was the key to Marib's existance in such a place. The stonework is of phenomenal quality, with sluices and anchor towers rising to a height of 18 metres. The dam was 750 metres across and held back water to a depth of 15m, which was used to irrigate an area of over 100 square kilometers 

Nikon F5, 17-35mm, Fuji Velvia 100