A strange tower inside the castle of Chios, close to the northeastern wall. Somehow, it seems isolated from the rest of the castle without an apparent functional relation with it.
For this reason it is presented separately in this site.

The castle of Chios was built by the Genoans around the end of the 14th century, most probably in the place where the old Byzantine fortress was located. The prevailing theory about the origin of the tower of Koulas is that it is the only remaining element of that older castle.

Another theory is that Koulas was one of the first viglas (watchtowers) of Chios. According to another hyothesis, it my have built by the Ottomans after the capture of the city in 1566.

Apart from the uncertainty about its origin, another particular feature of the tower is its shape. Its horizontal layout is not a circle but is more like a horseshoe, with the SE side of the otherwise cylindrical tower being flat. Also, it is obvious that for its construction spolia from older buildings were used,

Sources