"This feast was instituted by a mutual agreement of the Greeks and Russians at the time of the Greek Emperor Manuel and the Russian Prince Andrew in commemoration of the simultaneous victories of the Russians over the Bulgarians and the Greeks over the Saracens. In both of these battles, crosses were carried by the armies from which heavenly rays shone. It was therefore instituted that, on August 1, the Cross be carried first to the middle of the Church of the Divine Wisdom [Hagia Sophia] and after that, along the streets for the people to venerate as a commemoration of the miraculous help of the Cross in previous battles."

"This was not an ordinary cross but the true Honorable Cross which was kept in the church of the imperial court. On July 31, the Honorable Cross was carried from the imperial court to the Church of the Holy Wisdom of God and from there it was carried along the streets for the consecration of the earth and the air. Finally, on August 14, it was again returned to the church of the imperial palace."

Imagine walking through the streets of Constantinople in that procession! Does anyone know if there is a source on the exact route? Thanks! source: The Prologue from Ochrid http://www.westsrbdio.org/prolog/prolog.cgi