First Byzantine Period

Information about the Kythonia of the Christian Years is limited. The most important archeological finds are those of the remains of a Basilica, discovered recently near the Venetian Cathedral in the centre of Kasteli.

Various sources mention the Kythonia Diocese and the Bishop Kythonios, who participated in the Sardinian Synod in 343. Kythonia is mentiond among the 22 most important cities of Crete in the "Document of Ieroklis" in the 6th Century. The Kytonia Diocese is also mentioned in all the "Ecclesiastical Minutes" (taktica), before and after the Arabian Occupation.