There are two versions of the name of Kyparissia. In the first, the name comes from the fact that there are many cypress trees in the area, while in the second version, it comes from the hero of mythology, Kyparissos. According to legend, after he had killed a deer during a hunt, he became melancholic. Before he died, the gods heard his prayers, took pity on him and made him a cypress. At that time, god Apollo (friend of Kyparissos) and goddess Athena were worshipped. In fact, it was named “Kyparissia” Athena, and her temple was located in the current location of the church of the Holy Trinity.
During the Homeric years, Kyparissia was called “Kyparissientas” and belonged to the kingdom of Pylos. Later, the area was enslaved to Ancient Sparta along with the rest of Ancient Messinia. During the Turkish occupation, Arcadia (as Kyparissia was called in the Middle Ages) had a privileged position as a commercial centre of the region. A guard of 300 Algerians guarded its castle. Otto takes credit for the current name of the city.
Tombs of the Classical and Roman eras have been discovered in Kyparissia, while the Frankish castle is preserved at the top of Mount Psychro. Due to its location, the castle offers the visitor a unique view of the city and the wider area.

Source : https://messinia.mobi/en/article/poleis-kai-xoria-tis-messinias/kuparissia/68