Besides Hagia Sophia, other monuments of Byzantium ordered by Justinian were his equestrian statue in the middle of the Augustan, the Temple of St. Eirene, the church of Saints Sergius and Bacchus now known as Little Hagia Sophia, and the church-mausoleum of the Holy Apostles, where the graves of the emperors and the great saints of the Byzantine Church were laid to rest.
The Church of the Holy Peace or Hagia Eirene or Irene, still stands nearby Hagia Sophia. The name of Eirene means Peace in Greek, the sister of Hagia Sophia or the Holy Wisdom, who had her temple next to Eirene’s. Hagia Eirene’s floor plan is very characteristic of Byzantine architecture, as it consists of a large central nave divided by a wide arch into two parts, each one covered with a dome on pendentives. These two domes, equal in width, are of different height: one is raised on a cylindrical drum with windows, while the other, lower, rests directly on four arches. The higher dome is hemispheric, the other is oblong. The central nave is flanked by lateral naves, with groin vaults* and upper galleries covered with barrel vaults.
* The Groin vault results from the intersection of two barrel vaults at right angles. Geometrically, is generated by two orthogonal semi cylindrical surfaces whose lines of intersection, or groins, are arcs of ellipse that intersect at the apex. The figure shows the external structure of a groin vault (left) and its internal view (right). The letter “A” designates the groins.
The Church of Saints Sergius and Bacchus has a dome covering an octagonal room divided into segments. It seems that this church was built by order of Theodora, wife of Justinian, between 527-536.
The Church of the Holy Apostles was more popular and even was considered more national for the people born in Byzantium than the same church of Hagia Sophia. This temple is completely gone, now on its original settlement it is the mosque of Murad II. According to the Byzantine historian Procopius in his book “On Buildings”(Peri ktismatōn, Latin: De aedificiis) this church was in the form of two straight naves that crossed one another forming a cross, it was covered by domes although smaller than those of Hagia Sophia. On the four arches of the transept rose a spherical dome also with windows. Over the naves, on either side of the central dome, there were other four domes similar to the central one but without windows.
This church of the Holy Apostles in Byzantium is of extraordinary importance for Art History: it served as a primary model, more than any other Byzantine domed construction, for the building of other Western churches. Its simple floor plan, cross-shaped, with its five domes that support each other, was a an easily imitated type in cities that did not have the economic resources that were available for Byzantium. The first copy outside Byzantium of the Holy Apostles’ floor plan would be the Basilica of St. Mark in Venice and, likewise, following Saint Mark’s style, the French cathedrals from Auvergne were built.