      Tower of Pisa leans sideways because it was built on unstable soil. In 1173 construction started on the 180-foot bell tower, which is located in Pisa, a small town in the Italian province of Tuscany.The building began to lean as soon as the first three floors were completed.he leaning tower of Pisa costs €18,523,123 because it took almost 3 centuries to build and it kept sinking and they had to fix it over the years.