Kastri is the most important citadel (acropolis) of the early Cycladic II period (800 - 2300 BC) and probably the first location of Syros ever to be populated. It is about 45 minutes away on foot from Halandriani, another similar archaeological site of Ano Meria. Kastri was the kingdom of Ktesios, father of Eumaeus, a hero in Homer's Odyssey and an ever faithful person to Odysseus.
The total extent of the site is of about 3,5 to 5 daa / 0.86 to 1.24 ac. The archaeological excavations only revealed part of the ancient settlement. The buildings that have been found are small, stone built, rectangular or shaped as a D and they have one or two rooms. They are built close to one another and in some cases they share walls, thus forming clusters of constructions that are divided by narrow, irregular streets and small, open, common spaces.
The settlement was fortified with a 2 m / 6.5 ft thick wall made of small and medium sized rough stones. The walls of some houses were built against the inner part of this wall. The structure of the wall is strengthened by six horseshoe shaped towers. In a short distance, along this wall, there is a smaller, 1 m / 2.3 ft thick rampart which further hindered the access to the settlement.
The location of the settlement (over a steep cliff), the densely built houses, their unordered construction and principally the expansion of fortified settlements like Kastri prove that between 2450/2400 and 2200/2150 BC the area needed to be protected from attacks. This need resulted from the general economical and social changes and from the growing rivalry among the powerful cities of the islands or of the mainland. Indeed, the commercial and cultural exchanges among those cities are expressed in the architecture, in pottery and metalworking.
More specifically, silver, lead and bronze objects, clay melting pots and slate patterns for casting tools and weapons were found in a metalworking workshop in Kastri in the ancient settlement of Kastri.