combined Florentine and French army. With the original medieval fortifications beginning to crumble to French cannon fire, the Pisans constructed an earthen rampart behind the threatened sector. It was discovered that the sloping earthen rampart could be defended against escalade and was also much more resistant to cannon fire than the curtain wall it had replaced. The second siege was that of Padua in 1509. A monk engineer named Fra Giocondo, trusted with the defence of the Venetian city, cut down the city's medieval wall and surrounded the city with a broad ditch that could be swept by flanking fire from gun ports set low in projections extending into the ditch. Finding that their cannon fire made little impression on these low ramparts, the French and allied besiegers made several bloody and fruitless assaults and then withdrew. The new type of fortification also played a role in the numerous Mediterranean wars, slowing down the Ottoman expansion. Although Rhodes had been partially upgraded to the new type of fortifications after the 1480 siege, it was still conquered in 1522; nevertheless it was a long and bloody siege, and the besieged had no hope of outside relief because the island was close to the Ottoman power base and far from any allies. On the other hand, the Ottomans failed to take Corfu in 1537 in no small part because of the new fortifications, and several attempts spanning almost two centuries (another major one was in 1716) also failed. Two star forts were built by the Order of Saint John on the island of Malta in 1552, Fort Saint Elmo and Fort Saint Michael. Fort Saint Elmo played a critical role in the Ottoman siege of 1565 when it managed to hold out heavy bombardment for over a month. Eventually it fell, but the Ottoman casualties were very high, and it bought time for the relief force which arrived from Sicily to relieve the rest of the besieged island. The star fort therefore played a crucial and decisive role in the siege. After the fall of Venice to Napoleon, Corfu was occupied in 1797 by the French republican armies. The now ancient fortifications were still of some value at this point. A Russian–Ottoman–English alliance led at sea by Admiral Ushakov and with troops sent by Ali Pasha retook Corfu in 1799 after a four-month siege, when the garrison led by general Louis François