How old is the leaning tower of Pisa?

How old is the leaning tower of Pisa?

Explanation

The Leaning Tower of Pisa, or simply, the Tower of Pisa, is the campanile, or freestanding bell tower, of Pisa Cathedral.

It is known for its nearly four-degree lean, the result of an unstable foundation. 

Height: 57 m

Opened: 1372

Construction started: August 9, 1173

Architects: Diotisalvi, Guglielmo

Province: Province of Pisa

Materials: Marble, Rock

Architectural style: Romanesque architecture