Along the Land Walls - Strolling Through Istanbul: The Classic Guide to the City - page 352

We now come to Belgrad Kapısı, known in Byzantium as the
Second Military Gate. This is the largest of all the military gates and
in Byzantium it may have been used as a public gate, as indeed it has
ever since the Conquest. The gate took its Turkish name from the
fact that Süleyman the Magnificent settled in its vicinity many of the
artisans he brought back with him from Belgrade after his capture of
that city in 1521.
BELGRAD KAPISI TO SİLİVRİ KAPISI
The stretch of walls from Belgrad Kapısı to the next gate, Silivri
Kapısı, is also in good condition, with all 13 towers still standing
along the inner wall and only one missing in the outer. These towers
also have inscriptions recording repairs by Leo II, Constantine V and
John VIII. Silivri Kapısı is the first of the large public gates we come
to when walking from the Marmara. Like all of the public gates it
is double, that is with gateways through both the inner and outer
walls. The most memorable day in the history of the Silivri Gate
was 25 July 1261. On that day a small body of Greek troops led by
Alexius Strategopoulos overpowered the Latin guards at the gate and
forced their way inside, thus opening the way for the recapture of
Constantinople and the restoration of the Byzantine Empire.
THE SACRED SPRING OF BALIKLI
Silivri Kapısı was known in Byzantium as the Gate of the Pege
because it led to the famous shrine of the Zoodochus Pege, or the
Life-Giving Spring. The shrine, known in Turkish as Balıklı Kilise,
or the Church with Fish, is so called because of the fish that swim
in its sacred spring; it is reached by walking out from the gate along
Seyitnizam Caddesi for a short distance and veering right along
Silivrikapı Balıklı Caddesi. The shrine has been popular since the
early days of Byzantium, and several emperors built churches on the
site; the present one dating only from 1833. The outer courtyard is
particularly interesting because it is paved with old tombstones in
the curious Karamanlı script, that is, Turkish written in the Greek
alphabet. The inner courtyard is filled with the elaborate tombs of
bishops and patriarchs of the Greek Orthodox Church. The entrance