St. Peter's Basilica
At that time, there were only three very large domes in the whole world. One was far away in Constantinople on the church of Hagia Sophia and not many people in Italy had seen it. The other two domes were both very well known. One was the dome on the temple to the Ancient Roman gods, called the Pantheon. The other dome was built in the early 15th century (1400s) on Florence Cathedral by Filippo Brunelleschi. The dome of the Pantheon is 43.3 metres (142.06 ft) across and the dome of Florence Cathedral is about 42.1 metres (138 ft), but is much taller. Bramante's plan for the dome of St. Peter's was for it to be about as wide as the dome of Florence, and even taller.