From what is the Leaning Tower of Pisa made?

The Leaning Tower of Pisa was constructed from limestone and lime mortar to which marble was also added. Much of the limestone was covered in white marble from San Giuliano, but it was later replaced with other types of marble during restoration. The limestone has played a large part in keeping the tower from deteriorating as much as it could with the leaning issues of the tower.

The tower was not built at one time. There were many interruptions that slowed and sometimes halted the building. The first pause in construction was from lack of funds. There was nearly a century before construction began again, and it took nearly another to finish it.