Walls to keep out water are called dams and levees.
Levee
Levee
Levee
they both built the walls to keep them out with a wall
Rulers of different eras to build walls to keep the Mongols out.
The protective walls
the walls keep water inside
a dam
Usualy Brick or Stone walls are built in china.
The wall are built strong and high that less water can go on land
It was important for the mission walls to be built on rocks because so the walls could be stable.
That would be a dam or a levee.