In 1843 it was decided to build a series of diversion dams (barrages or weirs) across the Nile at the head of the delta about 12 miles downstream from Cairo, so as to raise the level of water upstream to supply the irrigation canals and to regulate navigation. This delta barrage scheme was not fully completed until 1861, after which it was extended and improved; it may be regarded as marking the beginning of modern irrigation in the Nile valley. To continue this, in 1909 by the barrage at Isnā (Esna) was completed