"Through this work, Giotto has become, together with Brunelleschi (dome of the cathedral of Florence) and Alberti, one of the founding fathers of Italian Renaissance architecture.
When Giotto died in 1337, he had only finished the lower floor with its external marble decoration of geometric patterns of white, green and pink marble.
The construction was continued by Pisano and In 1359 was completed by Talenti, Master of the Works from 1348 to 1359, who built the top three levels with the large windows. He did not build the spire designed by Giotto.
Each level is larger than the lower one and extends beyond it in every dimension so that their difference in size exactly counters the effect of perspective. As a result, the top three levels of the tower, when seen from below, look exactly equal in size (not in this photo though)."
"There are a couple of stories that Giotto died of grief for having given the bell tower as he said, “a too small bed for your feet.” It was also rumored that Giotto died of a heart attack because he feared that he designed the base too small to support the weight and the height. In reality, the base of the tower is more narrow than it should be, perhaps to give the effect of greater vertical momentum. But Giotto died at age 70, a ripe old age for the 14th century. (Later designs sustained the height and weight of the tower by constructing four internal polygonal buttresses at the corners.)"