As a corollary from this determination of the real site of the Hebdomon there follows the determination of the real site of the Cyclobion; and thus the correction of another of the mistakes into which students of the topography of Byzantine Constantinople have fallen. The prevalent opinion on the subject, since Du Cange[1212] propounded the opinion, has been that the Cyclobion was a fortress attached to the Golden Gate. But this could not have been the case, for the Cyclobion was at the Hebdomon. It was a fortification on the eastern headland of the bay which formed the Harbour of the Hebdomon,[1213] and, therefore, stood some two miles and a half from the Golden Gate. This explains how Theophanes[1214] describes the engagements between the Greeks and the Saracens, who landed at the Hebdomon in 673, as taking place between the Golden Gate and the Cyclobion. The fortress was so closely connected with the suburb that the latter is sometimes referred to under the name of the former. The Church of St. John the Evangelist at the Hebdomon, for example, is declared by one authority[1215] to have stood in the Cyclobion: “Ad Castrum autem Rotundum, in quo est Ecclesia, miræ magnitudinis, Sancti Evangelistæ Johannis nomini dicata.” Again, whereas John of Antioch[1216] represents the fleet of Heraclius as standing off the Hebdomon, the _Paschal Chronicle_,[1217] on the other hand, says the fleet was seen off the Round Tower. In all probability, the Cyclobion stood at Zeitin Bournou, on the tongue of land to the east of Makrikeui. It derived its name, Κυκλόβιον, Στρογγύλον Καστέλλιον (Castrum Rotundum), from its circular form,[1218] and was a link in the chain of coast fortifications defending the approach to the city. It was repaired by Justinian the Great, who connected it by a good road with Rhegium[1219] (Kutchuk Tchekmedjè), another military post, and drew upon its garrison for troops to suppress the riot of the Nika.[1220] There Constantine Copronymus died on board the ship on which he had hoped to reach the capital from Selivria, when forced by his mortal illness to return from an expedition against the Bulgarians.[1221] Whether the Cyclobion was the same as the “Castle of the Theodosiani at the Hebdomon,” mentioned by Theophanes,[1222] is not certain. On the whole, the fact that the two names are employed by the same historian favours the view that they designated different fortifications. The Theodosiani were a body of troops named in honour of Theodosius the Great.[1223]