Hydra, or Ydra, and in antiquity Hydrea, is one of the Saronic Islands of Greece, located in the Aegean Sea between the Myrtoan Sea and the Argolic Gulf. In ancient times, the island was known as Hydrea (Ὑδρέα, derived from the Greek word for "water"), a reference to the natural springs on the island.
There are numerous churches and six Orthodox monasteries on the island. Two particularly noteworthy monasteries are Profitis Ilias, founded in the 10th century, and Ayia Efpraxia. Both are on a hill overlooking the main harbour.
The island's cathedral is the old Monastery of the Dormition of the Virgin and sits on the quayside in the town. The monastery contains the tomb of Lazaros Kountouriotis, the richest sea captain on Hydra, who gave his entire fortune to support the Greek War of Independence.
During the Ottoman domination, the Turks had little interest on the island because of its lack of water. The island began to acquire a powerful merchant fleet during the 17th century but the plague of 1792 wiped out a great number of the population and those who survived moved away. Things improved for Hydra in the 18th century, when it became powerful and prosperous because of its highly developed commercial fleet, trading with all of Greece and even abroad, with France, Spain, and America.
The superiority of the island's fleet reached its peak during the Napoleonic wars and with the creation of the Merchant Marine Academy, was able to monopolize the sea transport throughout the Mediterranean. The inhabitants of Hydra were beginning to fear attacks from the Ottoman fleet so they used their wealth to fortify the harbor with bastions of cannons, and their fleet power during the Greek Revolution against the Turkish yoke. They participated in the Revolutionary secret alliance called "Philiki Etairia" (founded in 1814) and many wealthy sea-captains used their vessels as warships and helped the Revolution economically.
The heroism of their crews became famous all around Europe and is still honored today. Two of the most heroic figures of Hydra were the ship owners Andreas Miaoulis and Lazaros Koundouriotis, who contributed to the revolution. The superiority of the island's ships and the heroism of its inhabitants was one of the most determining factors in the success of the revolution.