Until this time the city of Massalia had guarded its independence and profited from its alliance with Rome. However, in 49 BC, when the struggle for the leadership of Rome began between Pompey the Great and Julius Caesar, the leaders of Massalia made the fatal decision to back Pompey. (See Caesar's Civil War). Caesar immediately sent an army to Massalia and besieged the city. He built long trenches around the town, as he had done against the Gauls at Alesia; and cut down the sacred forests of the Ligures to build siege towers. He also had a dozen warships built at Arles and his new fleet, led by his legate Decimus Junius Brutus Albinus, defeated the Massalian fleet off the isles of the Frioul archipelago, and blockaded the city from the sea. Disease ravaged the population. In September 49 BC, the soldiers of Caesar's legate Trebonius breached the walls of Massalia and captured it. The Massalians paid a heavy price for backing Pompey; the city lost its independence, had to surrender its warships and treasury, and was forced to give up all of its territories on the coast and interior, except for the Stoechades islands and Nice.