In the 12th century, monks began to excavate carp ponds - the Milicz Ponds were created. Waters were funnelled from the Barycz, a river that flows into the Odor after passing through a wide plain north-west of Wroclaw. The more than 100 Milicz Ponds represent the world's largest concatenation of ponds as the area spreads over 70 sq. km. The Barycz plain has a surface of 5,535 sq. km - ten times larger than Lake Constance.