probably thanks to the complexity of its river system and its consequent ease of defence. In the 7th century Pisa helped Pope Gregory I by supplying numerous ships in his military expedition against the Byzantines of Ravenna: Pisa was the sole Byzantine centre of Tuscia to fall peacefully in Lombard hands, through assimilation with the neighbouring region where their trading interests were prevailing. Pisa began in this way its rise to the role of main port of the Upper Tyrrhenian Sea and became the main trading centre between Tuscany and Corsica, Sardinia and the southern coasts of France and Spain.
After Charlemagne had defeated the Lombards under the command of Desiderius in 774, Pisa went through a crisis but soon recovered. Politically it became part of the duchy of Lucca. In 930 Pisa became the county centre (status it maintained until the arrival of Otto I) within the mark of Tuscia. Lucca was the capital but Pisa was the most important city, as in the middle of 10th century Liutprand of Cremona, bishop of Cremona, called Pisa Tusciae provinciae caput ("capital of the province of Tuscia"), and one century later the marquis of Tuscia was commonly referred to as "marquis of Pisa". In 1003 Pisa was the protagonist of the first communal war in Italy, against Lucca of course. From the naval point of view, since the 9th century the emergence of the Saracen pirates urged the city to expand its fleet: in the following years this fleet gave the town an opportunity for more expansion. In 828 Pisan ships assaulted the coast of North Africa. In 871 they took part in the defence of Salerno from the Saracens. In 970 they gave also strong support to the Otto I's expedition, defeating a Byzantine fleet in front of Calabrese coasts.
11th century
The power of Pisa as a mighty maritime nation began to grow and reached its apex in the 11th century when it acquired traditional fame as one of the four main historical Maritime Republics of Italy
