gainst Frederick Barbarossa in 1164 which ended with the Peace of Costanza in 1183; after which, the city began to expand rapidly (this is the period in which its famous towers were built) and it became one of the main commercial trade centers thanks to a system of canals that allowed large ships to come and go.
Depiction of a 14th century fight between the militias of the Guelf and Ghibelline factions in Bologna, from the Croniche of Giovanni Sercambi of Lucca.
In addition, in 1088 the Studio was established, now the oldest university in Europe, which could boast notable scholars of the Middle Ages like Irnerius, and, among its students, Dante, Boccaccio and Petrarca. In the 12th century, the expanding city needed a new line of walls, and at the end of the 13th century, Bologna had between 50,000 and 60,000 inhabitants making it the fifth largest city in Europe (after Cordova, Paris, Venice, and Florence) and tied with Milan as the biggest textile industry area in Italy.
The complex system of canals in Bologna was one of the most advanced waterway systems in Europe, and took its water from the Savena, Aposa and Reno Rivers. The main canals were Canale Navile, Canale di Reno and Canale di Savena. Hydraulic energy derived from the canal system helped run the numerous textile mills and transport goods. Now these canals are located under the city and some can even be visited on organized rafting tours.
In 1256, Bologna promulgated the "Paradise Law", which abolished feudal serfdom and freed the slaves, using public money. At that time the city centre was full of towers (perhaps 180), built by the leading families, notable public edifices, churches, and abbeys. In the 1270s Bologna's politics was dominated by Luchetto Gattilusio, a Genoese diplomat and man of letters who became the city Governor. Like most Italian cities of that age, Bologna was torn by internal struggles related to the Guelph and Ghibelline factions, which led to the
