The Bastions with Cannons in Hydra: On the Greek island of Hydra the bastions with cannons that were used for the protection of the harbor in due time war, can still be seen. During the 18th century, Hydra was in need of these cannons to protect the Island from the attacks of the Turkish fleet. The Greek ships were equipped with eight to twenty guns when on the Turkish frigate had up to eighty guns and a Turkish corvette ship up to thirty.
The Turkish fleet was superior quantitatively to the Greek so Hydra needed its cannons, in case they managed to get past the Greek ships. In the 19th century there was a probability for Hydra to use its cannons again, as the Greeks were at war with the Turks.
Fortunately, the Greek fleet had always managed to protect Hydra, and as a result, the cannons have not been often in use. The bastions with cannons seemed to be a necessary precaution in case Hydra actually got attacked. You can still see them today on the left and right side of the Harbor.