Justinian chose geometer and engineer Isidore of Miletus and mathematician Anthemius of Tralles as architects. The construction is described by Procopius's On Buildings (, ). Columns and other marbles were brought from all over the empire, throughout the Mediterranean. The idea of these columns being spoils from cities such as Rome and Ephesus is a later invention. Even though they were made specifically for Hagia Sophia, the columns show variations in size. More than ten thousand people were employed. This new church was contemporaneously recognized as a major work of architecture. Outside the church was an elaborate array of monuments around the bronze-plated Column of Justinian, topped by an equestrian statue of the emperor which dominated the Augustaeum, the open square outside the church which connected it with the Great Palace complex through the Chalke Gate. At the edge of the Augustaeum was the Milion and the Regia, the first stretch of Constantinople's main thoroughfare, the Mese. Also facing the Augustaeum were the enormous Constantinian thermae, the Baths of Zeuxippus, and the Justinianic civic basilica under which was the vast cistern known as the Basilica Cistern. On the opposite side of Hagia Sophia was the former cathedral, Hagia Irene.