even the moderate pay he was allowed by the Emperor having fallen in
arrear, he resigned his place and transferred his services to the Sultan,
who knew better how to value warlike knowledge. He now gave Mahomet
proof of his skill by casting the largest cannon which had ever been
fabricated. He had already placed one of extraordinary size in the
new castle of the Bosporus, which carried across the straits. The gun
destined for the siege of Constantinople far exceeded in size this
monster, and the diameter of its mouth must have been nearly two feet
and a half. Other cannon of great size, whose balls of stone weighed one
hundred fifty pounds, were also cast, as well as many guns of smaller
calibre. All these, together with a number of ballistae and other ancient
engines still employed in sieges, were mounted on carriages in order to
transport them to Constantinople. The conveyance of this formidable train
of artillery, and of the immense quantity of ammunition required for its
service, was by no means a trifling operation.

The first division of the Ottoman army moved from Adrianople in February,
1453. In the mean time a numerous corps of pioneers worked constantly at
the road, in order to prepare it for the passage of the long train of
artillery and baggage wagons. Temporary bridges, capable of being
taken to pieces, were erected by the engineers over every ravine and
water-course, and the materials for every siege advanced steadily, though
slowly, to their destination. The extreme difficulty of moving the
monster cannon with its immense balls retarded the Sultan's progress, and
it was the beginning of April before the whole battering-train reached
Constantinople, though the distance from Adrianople is barely a hundred
miles. The division of the army under Karadja Pacha had already reduced
Mesembria and the castle of St. Stephanus. Selymbria alone defended
itself, and the fortifications were so strong that Mahomet ordered it to
be closely blockaded, and left its fate to be determined by that of the