From Haghia Sophia to Beyazit Square - Strolling Through Istanbul: The Classic Guide to the City - page 134

The Milion, like its namesake in the Roman Forum, was the
point of departure for the great roads which ran out of the city
and was the reference point for their milestones. Here began the
Mese, or Middle Way, the main thoroughfare of ancient Constan-
tinople, which followed the course of the modern Divan Yolu. The
Mese, which was flanked for a good part of its length with marble
porticoes, led westward from the Milion along the ridge between the
First and Second Hills, atop which it passed through the Forum of
Constantine. Continuing westward, along the route of the Modern
Yeniçeriler Caddesi, the Avenue of the Janissaries, the Mese then ran
along the ridge between the Second and Third Hills and entered the
Forum of Theodosius, on the site of the present-day Beyazit Square.
Beyond there, the Mese divided into two branches, one of which
extended west and the other south-west. he western branch passed
through the Gate of Charisius, where it joined the Roman road to
Adrianople, now known as Edirne. The other branch passed through
the famous Golden Gate and linked up with the Via Egnatia, which
marched through Thrace, Macedonia and Epirus to the Adriatic. The
main thoroughfares of modern Stamboul follow quite closely the
course of these Roman roads built more than 15 centuries ago.
The thoroughfare between Haghia Sophia and Beyazit Square
continued to be one of the principal arteries of the town in Ottoman
times, for it was the main road from Topkapı Sarayı to the centre of
Stamboul. For that reason it is lined with monuments of the imperial
Ottoman centuries, as well as some ruined remnants of imperial
Byzantium. It is called Divan Yolu, the Road of the Divan, because of
the procession of dignitaries that passed along it whenever there were
meetings of the Divan, or imperial council, in the Second Court of
Topkapı Sarayı.
THE BASİLİCA CISTERN
The first monument on our itinerary is a short way down Yerebatan
Caddesi, the street that leads of half-right from Aya Sofya Meydanı
at the beginning of Divan Yolu. Almost immediately on the left
we come to a small building which is the entrance to an enormous
underground cistern, Yerebatan Saray, or the Underground Palace.