Cagliari is an Italian municipality and the capital of the island of Sardinia, an autonomous region of Italy. Cagliari's Sardinian name ''Casteddu'' literally means castle.

An ancient city with a long history, Cagliari has seen the rule of several civilisations. Under the buildings of the modern city there is a continuous stratification attesting to human settlement over the course of some five thousand years, from the Neolithic to today. Historical sites include the prehistoric domus de janas, very damaged by cave activity, a large Carthaginian era necropolis, a Roman era amphitheatre, a Byzantine basilica, three Pisan-era towers and a strong system of fortification that made the town the core of Spanish Habsburg imperial power in the western Mediterranean Sea. Its natural resources have always been its sheltered harbour, the often powerfully fortified hill of Monti Castru, the modern Casteddu, the salt from its lagoons, and, from the hinterland, wheat from the Campidano plain and silver and other ores from the Iglesiente mines.

Today the city is a regional cultural, educational, political and artistic centre, known for its diverse Art Nouveau architecture and several monuments. It is also Sardinia's economic and industrial hub, having one of the biggest ports in the Mediterranean Sea, an international airport, and the 106th highest income level in Italy (among 8,092 comuni), comparable to that of several northern Italian cities.

It is also the seat of the University of Cagliari, founded in 1607, and of the Primate Roman Catholic archdiocese of Sardinia, since the 5th century AD.