The disadvantages resulting from the transport of the Turkish ships into the harbour were at once felt. While continual pounding from the great cannon and other machines was going on at the landward walls and while feints were being made which kept the defenders always on the alert, to resist attacks or effect repairs, a portion of their forces had to be told off to defend the north-western walls facing the Golden Horn. Many attempts were made from these walls on the Horn, and from the Christian ships to destroy the Turkish vessels. Nearly every day as long as the siege lasted, some of the Greek or Venetian ships were told off to watch or attack them. Sometimes the Turks were chased to the shore: at other times the pursuers became the pursued.[330] [Sidenote: Building of bridge over Upper Horn.] To enable his troops to pass readily across the Golden Horn, Mahomet commenced and carried through with his usual energy the construction of a bridge over the upper part of it, near the place where the landward walls join those on the side of the Horn. This district was then known as Cynegion, and now as Aivan Serai.[331] The bridge was formed of upwards of a thousand wine barrels, all securely fastened together with ropes. Two of the barrels placed lengthways made the width of the bridge. Upon them beams were fixed, and over the beams a planking sufficiently wide to enable five soldiers to walk abreast with ease.[332] The object in placing the bridge so near the walls was, not merely to facilitate communications between the troops behind Pera and the army before the walls, but to attach to it pontoons upon which cannon could be placed for attacking the harbour walls. The paucity of the number of the defenders greatly alarmed the emperor and those around him who had gathered in council to meet the new dangers. They were compelled to recognise that this new point of attack, in the very place where, and where alone, the city had formerly been captured, required especial care, and accordingly they decided to send a strong detachment of Greeks and Italians to the north-west corner of the walls at Aivan Serai.[333] From the moment the Turks had gained entrance into the inner harbour they never ceased to harass the city on every side. During the next few days the cannonading against the walls was constant and the efforts to repair the damage equally persistent. [Sidenote: Provisions running short at commencement of May.] Barbaro mentions that on May 1 or 2 it was found that provisions were running short. The organisation for the supply of food to the soldiers was defective, and many complained that they had to leave the walls in order to earn bread for their wives and families. This led to the formation of what we may call a relief committee charged with the distribution of provisions. [Sidenote: Skirmishes between ships and besieged.]