Along the Land Walls - Strolling Through Istanbul: The Classic Guide to the City - page 346

inscriptions in Latin and Greek on the Mevlevihane Gate, anciently
known as the Gate of Rhegium. The Greek inscription merely gives
the facts, the Latin one is more boastful; it reads: “By the command
of Theodosius, Constantine erected these strong walls in less than two
months. Scarcely could Pallas herself have built so strong a citadel in
so short a span.” The pride is understandable, for the new defence
walls saved the city from Atilla, the Scourge of God, who withdrew
his forces and, instead, ravaged the western regions of the Roman
Empire.
Even though they are in ruins, enough remains of the Theodosian
walls to reconstruct their original plan. The main element in the
defence system was the inner wall, which was about five metres thick
at the base and rose to a height of 12 metres. This wall was guarded by
96 towers, 18 to 20 metres high, at an average interval of 55 metres;
these were mostly square but some were polygonal. Each tower is
generally divided into two floors which do not communicate with
one another. The lower stories were used either for storage or for
guardhouses; the upper rooms were entered from the parapet walk,
which communicated by staircases with the ground and with the tops
of the towers, where were placed engines for hurling missiles and
Greek fire at the enemy. Between the inner and outer walls there was
a terrace called the peribolos, which varied from 15 to 20 metres in
breadth, and whose level was about five metres above that of the inner
city. The outer wall, which was about two metres thick and 8.5 metres
in height, also had 96 towers, alternating in position with those of
the inner wall; in general these were either square or crescent-shaped
in turn. Beyond this was an outer terrace called the parateichion,
bounded on the outside by the counter-scarp of the moat which was
a battlement nearly two metres high. The moat itself was originally
about ten metres deep and 20 metres wide, and may have been flooded
whenever the city was threatened. All-in-all it was a most formidable
system of fortification - perhaps the most elaborate and unassailable
ever devised. Had it not been for the invention of gunpowder and
cannons these walls might never have been breached.
Most of the inner defence-wall and nearly all of its huge towers are
still standing, although sieges, earthquakes and the ravages of time