File:The fortifications of the Castle Larissa of Argos on September 5, 2020.jpg

The castle was named after the homonymous hill that rises above the city of Argos at 287 metres. Its strategic position, overlooking the most important city in the Argolid, as well as the maritime and terrestrial routes connecting the southeastern Peloponnese with Attica and the Aegean islands, was the reason for the fortification of the hill, already since the Prehistoric period. Remains of the Mycenaean fortification (13th cent. B.C.) are preserved in the citadel, while huge monolithic architectural parts of the Mycenaean fortification were embedded in second use in the Medieval fortification walls.

The present form of the castle was established in the Middle Ages, although uninterrupted use of the area is testified from the Prehistoric times until World War II. The ancient fortification walls, parts of which are still visible nowadays incorporated in the masonry of later times, constitute the main plan followed by Medieval fortifications. Defensive works comprise the citadel at the hilltop and an outer enclosure. Subsequently, and especially after the advent of artillery in the 15th century, the castle underwent major interventions and was reinforced by cylindrical towers.

Inside the citadel, there was probably the administrative building and military installations. A church of the first millennium has been also located, at the site of which a chapel dedicated to Virgin Mary was later constructed in 1174. A residential area developed in the outer ward, still unexplored. There were large cisterns in the areas of both wards of the castle. This layout was preserved until the end of the 14th century, with reinforcement works and minor interventions in Byzantine and Frankish times, establishing Larissa as one of the four most well-defended castles in the Peloponnese, as sited in the Chronicle of Morea.

Extensive works for the reinforcement of the fortifications were carried out during the 15th century, as a result of alternating Venetian and Ottoman rule of the castle, as well as the need to update defensive and architectural features due to the advent of artillery, including the construction of a cross-wall that cuts off the south part of the outer enclosure. The exterior wall is reinforced with large cylindrical towers with cannon embrasures. The walls of the citadel were raised and reinforced with three- and four-sided towers and an almond-shaped tower. Concurrently, the Byzantine gate is walled up and another gate is opened further to the west. After the mid-15th century the impressive cylindrical keep is constructed at the southwest corner of the citadel, nowadays in ruins.

During the 16th century the area of the outer enclosure to the south of the cross-wall is abandoned and deserted, while an outwork was added to the south of the citadel gate, thus creating an exterior courtyard. To the east of the outwork a passage is formed with a double gate.”