The fall of Konstantinoupolis in 1204 was similar to what happened to the rest of Greece as well as to Achaia which was conquered by Goulielm Sablittes on account of the conqueror of
Thessaloniki, Vonifatios Momferattos.
First they conquered Aigio then Patras and then Lower Achaia. Then, Achaia was divided into 48 feuds, 28 of which belonged to the Baron hood of Patras, 12 to the Baron hood of Kalavryta and 8 became the Baron hood of Vostitsa (of Aigio).
In 1257 part of the Baron hood of Patras became the Baron hood of Halandritsa, ruled by Gui de la Tremoille or Tremouille the castle of whom was named "Tremoulas". Later, following the death of Othonas de Tournet of Kalavrita, the Tremouille family took over the Baron hood of Kalavryta as well.
The area and the cities around Ladonas river belonged to the Baron hood of Akova along with Kerpini (Arcadia) and Strezova (Daphne) wich were taxed by Margarita of Passavas. Then, the famous "Bridge of the Lady" was built on Ladonas to join the two areas. In about 1276, the ruler of the Baron hood of Patras, Goulielmos Alamanos, sold the area to the Pope in Rome and it therefore came under the rule of the Latin Church until 1408 when it was allotted by the Pope to the Democracy of Venetia.
The Principality of Achaia or Moreas with Glaretza (ancient Kyllini) being its capital city, managed to boost economy in as short period of time and to bring a relevant peace between the conquerors and the conquered. The prince of Achaia, Godofreidos Villeardouinos, even fought the powerful Catholic Church which worked against the harmonious coexistence of the
natives and the foreigners.
New castles and towers were built, while the old ones were repaired to help the conquerors with the control of the various areas. They also expanded the fortress of Patras that was first built by Ioustinianos on the foundations of the ancient acropolis. They also built a temporary wall in Lower Achaia of the present Municipality of Dymi, the castle of Kalavryta and the towers of Halandritsa, Saravalio, Kamenitsa and Lyssaria, as well as the towers of Drepano and Psathopyrgos.
The mighty power of the Franks ended in 1259, after the battle of Pelagonia (Macedonia), where Goulielmos Villeardouinos the Second was defeated and captured by Michael Palaiologos the VIII who demanded and finally took the castles of Monamvasia, Mani and Mystras in order to release him. So, the Greek Byzantine Domain of Mystras was established, which administered the fight against the Frank domination, a fight that
ended successfully in 1430.
Achaia region was freed from the Frank domination in the spring of 1430, when Konstantinos Paleologos XI, who was later to become the Emperor of Byzantium, conquered the Castle of Patras.
