A series of small canals and ditches bringing water from a river deeper into the nearby farmland, which will improve fertility, but at the cost of constant management tying up manpower that could work the fields otherwise. Not very useful in already fertile regions, but very useful in less fertile ones.
- 15000 work hours
- 600 wood
- 25 metal
- 20 goods
- 200 minimum population to construct
- Full efficiency requires 400+ population
- Can only be built near rivers, can't be built in mountains or marshes.