The Torri dei Salvucci, in Piazza del Duomo in San Gimignano are also called the Torri Gemelle. They belonged to the most important Guelf family in the city, the Salvucci. They had become rich through usury and commerce.
Their massive and powerful appearance is no accident: the towers were meant to show the supremacy of the family to the entire city.
When they were built, they were taller than the 51 meters of the Rognosa Tower, but after a regulation in 1255 expressly forbade buildings higher than Rognosa, they were lowered.
Both towers have a square base and, like all medieval buildings, are designed for defence with very few openings. Even the entrance doors are extremely narrow.
The Salvucci's bitterest enemies were the Ardinghelli, Ghibellines who traded with Lombardy and the Orient. To compete with the rival family, they built two twin towers similar to the Salvucci's, right on the opposite side of the piazza.
The two Torri degli Ardinghelli also had square bases, but they weren't really twins. The tower on the right is a bit straighter and has a more austere, "medieval" look, with truly narrow openings. The other is larger and more imposing and has much larger windows.