Agathonisi is the northernmost island of the Dodecanese group of islands. In the ancient times it was called Ietousa, while Thucycides called the island Tragaia, Stravon Tragaiai and Plutarch TrAghia. More recent travellers refer to the island as Agatonissi. In the prehistoric period it was inhabited by Carians. The Ionians of Militos followed and later Dorians. By Decree of Duke Aggelos Komninos, Agathonisi was given as a present to the Monastery of Patmos. Till the 14th century it was a hideout of pirates, while in 1522 it became a dominion of the Turks. In the 19th century people from Patmos and Fournoi settled to Agathonisi. In 1912 the Italians followed the Turks and, following the unification of Dodecanese with Greece in 1948 it is an administrative part of the Municipality of Patmos. In 1954 is becomes an independent Community.
The older buildings present interesting architectural characteristics: They are oblong, ground floor, single room with roof made of canes and clay, built with dry wall and red soil.
The architecture of old houses is similar to Megalo Horio but with different arrangement. The houses are built in a cycle, round a common yard - atrium, and there are no windows looking outside.
Vaults (close to the Ai-Nikolas chapel)
Unique in the Dodecanese, these Byzantine structures have airshafts in their ceilings which suggest they were used as large storage structures for food.