Bonanno Pisano (Dates Unavailable) The St. Louis Arch, the Washington Monument, the CN Tower in Toronto, and the Burj Khalifa in Dubai all have massive foundations. The leaning tower of Pisa is an example of why the foundation is so important. Bonanno Pisano is given credit for the original architecture of the tower. Construction began in 1173, but since its completion in 1372, legions of engineers have spent centuries trying to fix the foundation problems that were baked in from its start. Pisa is located at the confluence of to rivers, on land that is soft and wet. A modern engineer would probably drive piles deep down into the unstable soil, until they anchored in stable soil or rock. This is how the city of Venice was built, using piles made of wood. With the Tower of Pisa, it looks like the builders simply dug a trench and used standard masonry footings. With soil so soft, this foundation is inadequate. So why is the tower standing at all? It is thought that a budgetary fluke saved it. When the tower was three stories tall, construction was interrupted for a century due to a lack of funding. This delay allowed the soil under the tower to consolidate and stabilize. Then, when construction resumed, attempts were made to straighten out the tower by making one side taller than the other. But the tower started leaning more and more. There have been several attempts to stabilize the lean over the years, none successful and several that made the lean worse. It wasn't until the twenty-first century that engineers found a solution in two parts. The tower leans to the south. So they used a process called soil extraction on the opposite side. They drilled down diagonally with augers and pulled out soil from underneath the north side. Gravity caused the tower to settle toward the north as the cavities filled in. They did not want to straighten the tower —that would kill tourism. They reduced the lean enough to bring the lower back into its safe zone. Then engineers installed a drainage system to extract excess water from the soil around the tower. Even though early engincers made mistakes initially, and nearly toppled the tower with several bad remediation ideas, their successors eventually found a working solution that saved the tower, lean and all.