Kea (Greek: Κέα), also known as Gia or Tzia (Greek: Τζια), Zea, and, in antiquity, Keos (Greek: Κέως, Latin: Ceos), is a Greekisland in the Cycladesarchipelago in the Aegean Sea. Kea is part of the Kea-Kythnos regional unit. Its capital, Ioulis, is inland at a high altitude (like most ancient Cycladic settlements, for fear of pirates) and is considered quite picturesque. Other major villages of Kea are the port of Korissia and the fishing village of Vourkari. After suffering depopulation for many decades, Kea has been recently rediscovered by Athens as a convenient destination for weekends and yachting trips. The population in 2011 was 2,455.
It is the island of the Cyclades complex that is closest to Attica (about 1 hour by ferry from Lavrio) and is also 20 km (12 mi) from Cape Sounio as well as 60 km (37 mi) SE of Athens. Its climate is arid, and its terrain is hilly. Kea is 19 km (12 mi) long from north to south and 9 km (6 mi) wide from west to east. The area is 129 km2 (50 sq mi) with the highest point being 560 m (1,837 ft) above sea level
The municipality Kea includes the island of Makronisos to the northwest.
During the classical period, Kea (Ceos) was the home of Simonides and of his nephew Bacchylides, both ancient Greek lyricpoets, of the Sophist Prodicus, and of the physician Erasistratus. The inhabitants were known for offering sacrifices to the Dog Star, Sirius and to Zeus to bring cooling breezes while awaiting for the reappearance of Sirius in summer; if the star rose clear, it would portend good fortune; if it was misty or faint, then it foretold (or emanated) pestilence. Coins retrieved from the island from the 3rd century BC feature dogs or stars with emanating rays, highlighting Sirius' importance.
During the Byzantine period, many churches were built and the prosperity of the island rose. It was Byzantine until, in 1204, it was captured by the Venetians in the wake of the Fourth Crusade. The Archbishop of Athens, Michael Choniates, came here in exile after his city fell to the Crusaders in 1205. It was recaptured by the Byzantines under Licario in 1278. In ca. 1302 during the Byzantine–Venetian War, it fell to the Venetians again, who built a castle on the ancient acropolis of Ioulis. In 1330 Cos became the seat of a Latin Church bishop but, since it is no longer a residential bishopric, it is today listed by the Catholic Church as a titular see. The earliest indication of it as a Greek bishopric is in a list by the Sicilian monk Nil Doxapatris of the second half of the 12th century and this may have been a later interpolation, since the list of the Greek bishops of Kea begins only at the end of the 16th century.
The island is famous for scuba diving with excellent visibility, rich marine life, awesome wall, cavern and wreck diving. Water temperature from 20-26 degrees Celsius. The highlight for recreational divers is the wreck of the unique paddle/wheeler steamship Patris which sank in 1868. She was a passenger steamer with length of 217 feet, in service in the Aegean Sea, owned by the "HELLENIC STEAMSHIP Co." based on Syros island, at thet time the capital of Greece. She hit the reef off Koundouros Bay at Makriopounda, Kea island on the 24th February 1868 with about 500 souls aboard. No casualties were reported owing to the proximity of land. She lays in -28m  The world famous wreck of the HMHS Britannic,, sister ship of the Titanic, located 1.5 nautical mile offshore, is for Tec divers, as the depth is approx. 120 metres (394 feet). SS Burdigala is a recently discovered wreck, 800 metres (2,625 feet) from the island's harbour, in -53m depth. For experienced divers only .Sunk in 1916, a 180 meters long ocean liner built in Germany by Blohm & Voss