According to Strabo, Viotia was the country with “three seas”, as it was surrounded by the Corinthian Gulf at south, Evoikos at northeast and Evripos at the southeast.
The archaeological sites of Viotia are extended, beyond its terrestrial area, to the rocky islands of the Corinthian Gulf. The number of cities along the northern coasts of the Corinthian Gulf in ancient Viotia, such as Krefsis (Livadostra), Tifa or Sifa (Alyki), Korsies (Hostia), Voulida (Zaltsa), Fokikos Medon, the White Houses, Antikyra (Palatia, Steno, Vroulias), as well as the islands of Kouveli, Makronissos (Diporto), Ampelos and Daskalio demonstrate the existence of a sea road with sheltered and safe harbors offering a passage to the inland for commercial or military purposes.
According to archeological data, the habitation of Thisvi has been continuous from the Mycenaean period to the Christian times. As mentioned in mythology it took its name from the nymph Thisvi, the daughter of Asopos god. Homer in Iliad includes Thisvi among the cities that took part in the Trojan War. There, it calls it "politrirona" because of the large number of pigeons living in the area. At the end of the Archaic period it was an autonomous city and was a member of the Boeotian Community (about 525-520 BC). Thisvi participated in the Third Macedonian War (172-168 BC), supporting the Macedonian king Perseus. But, shortly after its beginning, Thisvi was besieged and finally conquered by the Romans. In the 2nd century AD, Pausanias, describing Thisvi, gives information on the existence of the sanctuary of Hercules and the organization of a celebration in honor of him. Particular reference is made in the presence of an ancient embankment that functioned as a drainage project.
In Thisvi there are remains of two fortified citadel. The oldest is located on the hill north of the present village, where the position of Ancient Thisvi. It is about the Palaiokastro or Upper Acropolis, the walls of which are characterized by at least four building phases, from the Archaic period to the Late Roman and Early Christian years. However, it continued to be in use later in the Middle and Late Byzantine periods. The Lower Acropolis, also called Neokastro, dates back to the Hellenistic period, with retrofits during the Byzantine era. Its architectural remains are detected on the south side of the site.
Out of the walls, in the rocky hills, a large number of burials have been carved. Their dimensions vary depending on the arcosols that have been formed inside them, while, individual arcosols also exist. They are dated in the Early Christian period. However, they are not unlikely to belong to an earlier era - at least some of them - until the first Christian era.
The historical testimonies of Thisvi during Byzantium are inadequate and do not substantiate its particular characteristics and the way in which its society is organized. Its ancient name was in use until the Early Christian period. At the end of the Late Byzantine period and during the Ottoman times it reappears under the name "Kakosi", until 1915, when the settlement was renamed to Thisvi. However, the unbroken habitation of the area during the Middle and Late Byzantine period is revealed by the archaeological superficial, mainly, research carried out at Thisvi. From the middle of the 19th century, the ongoing study and the re-association connects Thisvi with the place-name "Kastorio", which refers to the life of Saint Loukas (10th century). The identification of Byzantine Thisvi with Kastorio is mainly due to a tax record of 1466/1467. Here is a second name for the village of Kakossi, also called "Kastoria". Kastorio is no doubt considered to be the birthplace of Saint Lοuκas, the founder of the homonymous monastery of Viotia. His biography describes the escape of his ancestors from Aegina island (in the middle of the 9th century, for the fear of the pirates) to the port of Vathy, as it is today called Thisvi’s seaport. The adjacent mountain, Saint John or Agiannis, is also identified with the place where the Saint led his ascetism and is called in its biography as "Ioannitzi" or "Jannitzi".
Commercial and economic importance of Thisvi
Significant for the trade that took place in the natural harbors of Thisvi is the existence of organized residential complexes in the coastal rocky islands, such as Kouveli and Makronisos. The communication of its harbors with the coasts of the Peloponnese and the fact that the access to Central Greece was much shorter through Thisvi contributed to the commercial importance of the city. Through Thisvi the travelers between East and West avoided the tour of Attica and the Peloponnese. The harbors of Thisvi and Agios Ioannis in the early of 20th century were still active as in 1912 there was a customs office there and a small village of 62 inhabitants in 1934. The customs served corn transportation from Kopaida (Central Greece) to the opposite coasts of Peloponnese.