In northern and central Italy, the traveler is often struck by the spindly towers constructed in medieval times, many around the 13th century. Sometimes, as in the case of San Gimignano, a small city might, from a distance, look very much like a modern vertical city space--as if you'd spotted a misplaced and ethereal Manhattan.
A (very) short history of medieval Italy
After attempts by Franks, Goths, and Lombards to conquer and unify post Roman Italy, the collapse of state power and relative peace from outside invasion in the 10th through the 14th century saw a doubling of the Italian population and a great expansion of both city size and merchant capitalism. With the state weakened, the ruling elite changed; the bishops and agents of the state giving way to knights, feudal magnates, and episcopal clergy who formed itself into local communes. Those aristocratic communes and the city states they administered became the ruling forces in various cities throughout Italy.
The communes were associations of men who collectively held public authority and ruled and administered their cities; a few elite families could control a city. But by the end of the 12th century, competitive rivalries between families started to turn deadly, and by the end of the 12th century it became common to build defensive towers as fortresses and lookout spots as members of the aristocracy retreated into the safety of their clans.
These clans entered into alliances with other associations, and members collectively ruled sections of the city, with "their" tower or towers in the center. Access of members to the tower or towers was by underground passage or bridges from the upper stories of their houses to upper windows of a tower. The towers stood as a symbol of a clan's power and influence, the higher the tower the more influential a clan was, but they also served as safe havens and lookout spots for a nervous aristocracy.
As the clans quarreled and quarters dominated by them degenerated into armed war zones, the neighborhoods and their emerging middle classes began to organize themselves into societies and guilds to protect the value of their labor and to combat the street violence promoted by the nobility. The aristocratic communes started losing power to popular communes. The popolo eventually won out, seizing power from the aristocracy 500 years before the French Revolution.
To the traveler, the long period of independence of the Italian cities and regions gives each a unique character; traveling through Italy is like burrowing through a complex layer cake of historical artifacts bound together by a fierce adherence to local traditions. The food of Italy, for example is not Italian, it's regional, as are many of the architectural traditions and festivals. It's a delicious combination that delights the senses at every turn. Bring a fork and a camera.
Medieval Towers for the Traveler to View
You'll see towers in the "centro storico" of many Italian cities.
The city most noted for its towers is San Gimignano. 14 of its original 72 towers survive (pictures).
Perhaps the best known tower is Torre degli Asinelli in Bologna, which stretches 97.20 meters into the sky and leans by two meters. It shares a space in Bologna's Piazza Maggiore with La Torre della Garisenda at 48.16 meters. (picture)
The history above has been drawn largely from A Traveller's History of Italy by Valerio Lintner . I highly recommend the book for visitors interested in the history that drove the innovations and cultural artifacts they see in their travels.