For what god did ancient Greeks build the largest temple in a city-state?

The temples were built to God Zeus, who was the supreme God in most of the city-states.

Explanation:

Statues of Zeus were built around the Ancient Greece, but the most famous one was the one in Olympia, that was built in the 5th Century BC. The statue that was built also in his honor was regarded as one of the seven wonders of the Ancient world.