View of that piazza from the highest tower, Torre Grossa.
And a couple more views.
I went to a Cartier-Bresson exhibition here which was pretty amazing. While there I was able to get this view, with 8 or 9 towers in it - it's very difficult to get numerous towers in one photo.
So here's a little tower history.
"San Gimignano rises on top of a hill 334m above sea level, clearly visible in the distance with its many towers. Today 13 towers remain of the 72 towers of the fourteenth century, when every well-off family built a tower to show its economical power (many of them are still visible in the buildings, even if they were cut off).
"In medieval times, the tower was the higher symbol of power, mainly because the building process was not simple or cheap at all. Materials needed to be dug and transferred to town, and the building site arranged. Only the richest families of merchants and moneylenders could afford the works of construction."