Ypati was fortified for the first time in Hellenistic times. Parts of this fortification have been found in many areas around the Castle and the modern settlement. The fortification was renewed in the Early Christian era by Emperor Justin (527-565 AD). In 869 Ypati was referred to an ecclesiastical session for the first time under the name of New Patras along with Lamia, which was then known as Zitouni. In 1204 he was captured by the Frank crusaders and in 1218 passed into Byzantine sovereignty as Head of the despots of Epirus. In 1267 he was bequeathed to Ioannis Aggelos Doukas Komninos of Nothos, who fortified the Castle and made Ypati the seat of the state in the High Court of the Great Wallachia, which extended to western Macedonia.
In 1275, Ypati Castle accepted an attack from John Palaiologos, a Byzantine general, head of 30,000 men. Its strong fortification prevented its occupation by raid. John escaped and summoned for help from the Frank, Duke of Athens, who arrived in New Patras, chief of knights, and dissolved the siege. The castle remained in the sovereignty of John's descendants until 1318, when it got passed down into the hands of the Catalans, who formed the duchy of Athens and New Patras. In 1393 he was captured by the Turks, led by Sultan Vayiazit. During the Ottoman period of domination, it was called Patratziki (Small Patras) and it was the headquarters of a particular province.
Several remnants of this mighty fortress, fortified vigorously and weather beaten is still intact today. In particular are the ruins of a round tower, which up until today its age is still disputed - it is unknown in other words, whether it was constructed by Greeks, Franks or Catalans.
The church of Agia Sophia was built on the site of an older temple, probably dating back to the early Christian period. Architectural members of early Christian, Byzantine and post-Byzantine times have been embedded on its facades, while on the south side baptism remains from the 5th century have been found.