During which centuries was the Leaning Tower of Pisa built?

Player #25874027, It started to lean during construction. Some levels part way up are not even-sized as they tried to make those bits more upright. From 1990s they removed some of the substrate from underneath one of the sides to lessen the angle from a critical point.

The angle had slowly increased over the centuries. Around the turn of the last century work was done to decrease the angle to less than 4 degrees. No one wants to totally straighten it. It is too historic.