These pictures show the moment British archaeologist Leonard Woolley and his wife, Catherine, discovered the 6,000-year-old drainage system of the city of Ur, ancient Mesopotamia. The network of terracotta pipes collected rainwater and human waste and is one of the oldest plumbing systems in the world. The pictures were taken in 1930 when the ancient city had been excavated. The third picture reveals knee and t-joints unearthed at the Temple of Bel, in Nippur - another ancient Sumerian city and