the tower of pisa is a part of what cathedral???

Answer 1

The Tower of Pisa ( or Leaning Tower) is the bell tower of the Cathedral of Pise. Together with the Baptistry all these 3 monumental works of art are forming the whole of the famous 'Campo dei Miracoli' (Field of Miracles).
The construction of the Tower construction began in the August of 1173 and continued (with two long interruptions) for about two hundred years, in full fidelity to the original project, whose architect is still uncertain.
In the past it was widely believed that the inclination of the Tower was part of the project ever since its beginning, but now we know that it is not so. The Tower was designed to be "vertical" (and even if it did not lean it would still be one of the most remarkable bell towers in Europe), and started to incline during its construction.
Both because of its inclination, and its beauty, from 1173 up to the present the Tower has been the object of very special attention. During its construction efforts were made to halt the incipient inclination through the use of special construction devices; later colums and other damaged parts were substituted in more than one occasion; the recent interventions have being carried out within the sub-soil in order to significantly reduce the inclination and to make sure that Tower will have a long life.

Answer 2

As you can see in this photo...
http://img263.imageshack.us/img263/3617/campodeimiracoli8al.jpg
...(Campo dei Miracoli), the Tower of Pisa is the bell tower of the Dome. In Campo dei Miracoli you can see the dome, the tower, the baptistry anche the cemetery.