Bologna has retained a marked medieval aspect; many streets are arcaded. Noteworthy structures include the Palazzo Comunale (13th and 15th-16th cent.); the Renaissance-style Palazzo del Podesta; the palace of King Enzio (13th cent.); the Basilica of San Petronio (begun in 1390), with a 15th-century doorway by Jacopo della Quercia; the Church of Santo Stefano; the Church of San Giacomo Maggiore (founded 1267, major alterations in the 15th cent.); the Church of San Domenico (early 13th cent.); and the Archiginnasio (once the seat of the city's noted university and now a library). Bologna also has an archaeological museum; an art gallery, with works by Bolognese artists, including Francia, the Carracci, and Guido Reni; and a nuclear research institute. The city's observatory (founded 1712) is the oldest in Italy. On hills near the city are the Renaissance Church of San Michele (in Bosco) and a former Carthusian monastery.

Originally an Etruscan town called Felsina, it became a Roman colony in 189 b.c. The city came under Byzantine rule in the 6th cent. a.d. and later passed to the papacy. In the early 12th cent. a strong free commune was established. The victory of Bologna over Emperor Frederick II at Fossalta (1249) added political power to the city, then known chiefly as an intellectual center. Bologna's famous university originated (c.1088) with its Roman law school (founded a.d. 425), where Irnerius and Accursius taught; medical and theological faculties and courses in the liberal arts were added in the 14th cent. In later years those active at the university included Malpighi, Galvani, and Marconi.

In politics the rivalry between the Guelphs and the Ghibellines enabled several ambitious families to seize power (13th-15th cent.). The Pepoli were succeeded by the Visconti of Milan and, after a short period of papal rule, by the Bentivoglio (1446). In 1506, Pope Julius II reestablished papal rule. The coronation of Charles V at Bologna (1530) was the last imperial crowning by a pope. The Council of Trent met at Bologna in 1547-48. Papal rule was interrupted in 1797, when Bologna was made the capital of the Cispadane Republic, but resumed in 1815 after the Congress of Vienna. There were unsuccessful revolts in 1831, 1843, and 1848, and in 1860 Bologna voted to unite with the kingdom of Sardinia. The city was heavily bombed by the Allies in World War II. In 1980 a terrorist bomb killed 85 people in the city.