The Leaning Tower of Pisa is the campanile, or freestanding bell tower, of the cathedral of the Italian city of Pisa. It is situated behind the Cathedral and it is the third structure in Pisa’s Campo dei Miracoli (field of Miracles).
Although intended to stand vertically, the tower began leaning to the southeast soon after the onset of construction in 1173 due to a poorly laid foundation and loose substrate that has allowed the foundation to shift. [ wikipedia link ]
Contributed by Kevin & John G.