Chlemoutsi (Greek: Χλεμούτσι or Χλουμούτσι Chloumoútsi), also known as Clermont, is a medieval castle in the northwest of the Elis regional unit in the Peloponnese peninsula of southern Greece, in the Kastro-Kyllini municipality.

In Ottoman times, minor additions were made to provide platforms for artillery, but the castle progressively lost its significance and was completely deserted by the late 18th century.

Geoffrey had asked the clergy, which owned almost a third of the Principality's lands but was not obliged to render military service, for additional donations to help defend the realm.

When the clergy refused, claiming that they owed allegiance only to the Pope, Geoffrey confiscated Church property, and began construction of Chlemoutsi with the new funds.

These three sites were the administrative heart of the Principality and, along with the fortress of Beauvoir or Pontiko at Katakolo further south, served to secure control of the fertile plain of Elis, which formed a major part of the princely domain (along with Corinthia and the Evrotas Valley in Laconia).

The latter's acquisition of some of the "most fertile lands and the most powerful fortress in the Morea", in the words of the French medievalist Antoine Bon, in addition to the wealth he had inherited from his first marriage, worried King Charles.

On 25 September 1281, an agreement was reached whereby Chlemoutsi and Kalamata were ceded to the princely domain in exchange for half the lands of the recently deceased Leonard of Veroli, comprising estates in both the Morea (in Elis and Messenia) and Italy.

[12] In c. 1311, the sole surviving daughter of William II Villehardouin, Margaret, sought, by virtue of her descent, to claim the Principality, or at least a portion of it, including Chlemoutsi and Kalamata, from the Angevin Kings of Naples who had controlled it since 1278.

[14] In 1418, Glarentza and Chlemoutsi passed into the hands of Carlo I Tocco, who began to expand his territories in the Morea at the expense of Prince Centurione II Zaccaria.

[12] The bastard son of Centurione II, John Asen Zaccaria, was also imprisoned at Chlemoutsi, but managed to escape in 1453 and lead a rebellion against the Byzantine Despots of the Morea.

In 1701 the provveditore generale Francesco Grimani proposed that it be destroyed, as it was too far from the sea—a vital concern for the maritime-minded Republic—and difficult to defend, and recommended that Glarentza, by then abandoned and ruined, be rebuilt instead.

[12] Its location, on a small plateau of 226 metres (741 ft) above sea level near the modern village of Kastro-Kyllini, gives it a commanding view of the surrounding countryside, encompassing the coastal plain of Elis and reaching to the Ionian Islands of Zakynthos and Cephalonia and even to the coast of Aetolia-Acarnania on the Greek mainland.

[21][22] The view from this location and the scale and quality of its construction prove, according to A. Bon, that Chlemoutsi was not built as a citadel for Glarentza, but that it fulfilled an independent military role, that of securing control over the wider region.

The wall is built of limestone masonry, with little evidence of brick or tiles, topped by a small inner parapet and Ottoman-built crenellations, now largely ruined.

[28] Roughly halfway between the southwestern corner and the keep, the wall abruptly turns inwards for about 5 metres (16 ft) around an Ottoman-built tower before continuing east and then northeast to join the keep.

The upper storey features large galleries with ovoid barrel vaults "of immaculate poros ashlar" (Andrews), supported by side walls of limestone blocks and by regularly spaced transverse arches every 7–10 metres (23–33 ft).

The galleries also feature niches and fireplaces similar to those of the outer curtain wall and the associated buildings, reinforcing the "stylistic uniformity" (Andrews) of the castle.

[31] Chlemoutsi was well suited for a princely residence: its halls, arranged around the inner courtyard, were spacious, comfortable, and well-lit, cool in the summer and provided with several fireplaces for the winter months.