Constantinople, though it has ceased to be the capital city of a maritime power, has never lost the advantages of its unique maritime position. The sea, with its currents and its storms, has always been its first natural protector. Only once has the city been captured from the sea. But this has not meant that defence was necessary only for the landward approach. Byzantium had its sea-walls: they were enlarged by Constantine, and in 439 Theodosius II. completed them by carrying them on to meet the land-walls, which ended then at Blachernae northwards and by the Golden Gate on the south. During the middle ages they constantly needed repair, notably after the arctic winter of 763-4, when huge ice-floes thronged the Bosphorus and the Golden Horn, and even broke over the wall at the point of the Acropolis (Seraglio point). In the ninth century again Theophilus made a thorough restoration, which is recorded in many inscriptions still to be seen on the wall by the Dierman Kapoussi at the foot of the Seraglio gardens. Among later restorations are those of Leo the Wise and his brother Alexander: a tower, near Koum Kapoussi, bears the inscription: + ΠΥΡΓΟΣ ΛΕΟΝΤΟΣ Κ ΑΛΕΞΑΝ + and it is here, it has been suggested, that the Cretans held out in 1453 till Mohammed gave them special terms and allowed them to depart with all the honours of war. Michael Palæologus, after the recovery of the city from the Latins, began an inner sea-wall, but no traces of it, Professor van Millingen says, have survived. In 1351 again all the seaward walls were repaired, and all the houses that had been built between them and the sea were destroyed. It appears that the strip of ground originally outside the walls was smaller than at present, considerable silting having taken place during the last five centuries. The Venetian fleet in 1203 drew near enough to the walls to throw a flying bridge from the ships to the ramparts.