From the box:
Originally designed as part of the town's defenses, the towers later became status symbols. Only the very rich aristocratic families were granted permission, so that a Clan Tower was regarded as a demonstration of wealth and social status. When the guilds of craftsmen and artisans gained the upper hand in the running of the town, they tried to discourage the construction of new towers. But San Giminano's most influential families still managed to secure building permission.
Each player assumes the role of the head of an aristocratic family. By strategically deploying members of the family, the players seek to gain influence in the various guilds and to construct as many towers as possible.