Poor Foundation
The most famous poor foundation in the world is the Leaning Tower of Pisa in Italy. The tower began to sink after construction progressed to the third floor in 1178. Scientists travel yearly to measure the building's slow descent. They report that the 179-foot tower moves about one-twentieth of an inch a year. The tower threatens to fall onto the nearby ristorante, where scientists now gather to discuss their findings. Quite significantly, the word "pisa" means "marshy land," which gives some clue as to why the tower began to lean even before it was completed. Also--its foundation is only 10 feet deep!
In May 2008, after the removal of another 70 metric tons (77 short tons) of earth, engineers announced that the Tower had been stabilized such that it had stopped moving for the first time in its history. They stated it would be stable for at least 200 years. All because of a poor foundation!
(Source: Leaning Tower of Pisa, http://www.bible.org/illus.php?topic_id=579)