Already, on May 16, the besieged had discovered that the Turks were attempting to undermine the walls and thus enter into the city. Zagan Pasha, the renegade Albanian, in command of Mahomet’s army in Pera and opposite the walls from Caligaria to the Horn, had under him a number of miners, who had been brought from Novo Brodo in Serbia and who possibly were Saxons brought to that country to work in the silver mines. These men took in hand the task of undermining. They commenced their work at a distance sufficiently far removed not to be observed by the besieged. Probably the first place attacked was between the Adrianople Gate and Tekfour Serai. They endeavoured to undermine the foss and the Outer Wall.[336] When this failed a second attempt was made against the walls of the quarter called Caligaria, and this, says Barbaro, because in that place there were no enclosures or, as he calls them, ‘barbicans,’ the wall being single and unprotected even by a ditch. This description enables us to identify the place as the wall running at right angles to the northern end of the foss. An Austrian named John Grant, who acted under the Grand Duke, took charge of the counterminers and succeeded in finding and entering the Turkish mine, where he and his men burnt the props. The works fell in and suffocated a number of Turkish workmen. The incident greatly alarmed the citizens, who feared that on future occasions Grant might not be fortunate enough to discover the mine before the Turks had entered by it or had blown up a part of the walls. Fortunately, the rocky character of the ground prevented the miners from meeting with any notable success. Phrantzes states that the only damage done by the Turks in mining was to destroy part of an old tower, which was soon repaired by the defenders.[337] [Sidenote: Construction of a turret, May 18.]