To hold its island capital in a closed lake basin, the Mexica built a system of raised causeways, sluice-gated dikes and aqueducts across Lake Texcoco. The great dike attributed to Nezahualcoyotl, some sixteen kilometres long, walled off the brackish eastern lake from the freshwater western basin that fed the chinampas and the city. Causeways carried roads, controlled flow and could be cut to defend Tenochtitlan, while twin masonry aqueducts brought spring water from Chapultepec. The works integrated flood defence, water supply and salinity control at the scale of an entire basin.
It is one of the largest hydraulic-urban schemes of the pre-Columbian world, sustaining a city of perhaps 200,000 on an island in a saline lake. The basin's later flooding under colonial neglect underlines how load-bearing the indigenous waterworks had been.