It rose to become an economic powerhouse, a commercial center whose merchants dominated Mediterranean and Italian trade for a century, before being surpassed and superseded by the Republic of Genoa.

During the High Middle Ages the city grew into a very important commercial and naval center and controlled a significant Mediterranean merchant fleet and navy.

Pope Gregory VII recognized in 1077 the new "laws and customs of the sea" instituted by the Pisans, and Holy Roman Emperor Henry IV granted them the right to name their own consuls, advised by a Council of Elders.

During the period of great political and economic expansion, the republic had its own consoles with commercial farms and warehouses in many seaside cities: Gaeta, Naples, Salerno, Messina, Palermo, Trapani, Mazara del Vallo and in Tunis.

[4] The important Pisan port, key to the entire state economy, was defended by some towers on the sea and on the land side by a fortified system of fortresses on the hills behind, having Lari as the seat of the captaincy of the upper hills, Crespina, Fauglia, Castellina, Rosignano and finally Livorno with the plan of Porto Pisano, essential outlet to dominate the western Mediterranean, while the area that intersected the Arno with the Valdera was defended by the castles of Appiano, Petriolo, Montecuccoli and finally, by order of foundation, that of Ponte di Sacco (1392).

The main strongholds were the Verruca fortress, near Calci, which served as the cornerstone of the mountain defensive system on the Lucca border that ran from the ancient lago di Bientina to the Serchio with the castles of Caprona, Vicopisano, Asciano and Agnano.

[4] The Maremma territory south of the port of Vada was administered in the name of the republic by the Pisan counts of Della Gherardesca family with the castles located in numerous cities such as of Guardistallo, Bibbona, Riparbella and Suvereto.

[8] With Florence's domination began an unstoppable decline of the city which, in the past centuries had spread its Romanesque architectural style, even in Sardinian churches.

Suffocated of the commercial and merchant traffic that had characterized its efficiency for centuries, some of the most important Pisan families—such as the Alliata, the Della Gherardesca, the Caetani and the Upezzinghi—emigrated to other Italian city-states to escape the Florentine domination, in particular to the Kingdom of Sicily.