Procopius, Of the Buildings of Justinian
“ The church consequently presented a most glorious spectacle, extraordinary to those who beheld it, and altogether incredible to those who are told of it. In height it rises to the very heavens, and overtops the neighbouring buildings like a ship anchored among them: it rises above the rest of the city, which it adorns, while it forms a part of it, and it is one of its beauties that being a part of the city, and growing out of it, it stands so high above it, that from it the whole city can be beheld as from a watch-tower. ”
