From the Galata Bridge to Sehzadebasi - Strolling Through Istanbul: The Classic Guide to the City - page 224

various streams and lakes outside the city, appears to have entered
through subterranean pipes near the Edirne Gate and to have been
led underground along the ridge of the Sixth, Fifth and Fourth Hills
to a point near the present site of the Fatih Mosque. From there
the water was carried by the aqueduct across the deep valley that
divides the Fourth from the Third Hill. On the Third Hill, near
the present site of Beyazit Square, the water was received in a large
cistern, the nymphaeum maximum, from which it was distributed to
various parts of the city; this nymphaeum seems to have been not
far distant from the modern taksim which distributes the present
water supply from the Terkos Lake. The length of the aqueduct was
originally about one kilometre, of which about 900 metres remain,
and its maximum height, where it crosses Atatürk Bulvarı, is about
20 metres. The aqueduct was damaged at various times but was kept
in repair by the emperors, both Byzantine and Ottoman, the last
important restoration being that of Mustafa II in 1697. The long
march of the double arches across the valley has a grand and Roman
look, and is almost as essential a characteristic of the city's skyline
as the great procession of mosques that crowns the ridge along the
Golden Horn.
Continuing on along Atatürk Bulvarı under the aqueduct, we
soon come to the Şehzadebaşı intersection, which we cross to the
south-west corner. This intersection is approximately the site of the
ancient Forum Amastrianum, where public executions were held in
the days of Byzantium. At the Forum Amastrianum, the Mese divided
into two branches, one of which followed much the same course as
Şehzadebaşı Caddesi, while the other went along roughly the same
route as Atatürk Bulvan to the Forum Bovis, the modern Aksaray.
THE CHURCH OF ST. POLYEUKTOS
Perhaps the best thing that can be said about the Şehzadebaşı
intersection is that it has at least advanced the cause of archaeology.
For when the ground was being cleared for the underpass in 1960,
there came to light the extensive ruins of an ancient church; we see
these just to the right of the underpass road to Aksaray. An excavation
was taken in hand by Dumbarton Oaks under the direction of Mr.