Slowly the Romans had occupied most of Sicily; in 250BC they besieged the last two Carthaginian strongholds Lilybaeum and Drepana in the extreme west. Repeated attempts to storm Lilybaeum's strong walls failed, as did attempts to block access to its harbour, and the Romans settled down to a siege which was to last nine years. They launched a surprise attack on the Carthaginian fleet, but were defeated at the Battle of Drepana; Carthage's greatest naval victory of the war. Carthage turned to the maritime offensive, inflicting another heavy naval defeat at the Battle of Phintias and all but swept the Romans from the sea. It was to be seven years before Rome again attempted to field a substantial fleet, while Carthage put most of its ships into reserve to save money and free up manpower.