Kyrrhos/Cyrrhus in Syria, established during the Hellenistic period, is known as a Seleucus Nicator foundation. The polygonal rampart attributed to this period has been observed over nearly the entire city, except on a large part of the southern fortification. Since 2006, the Lebanese and Syrian Archaeological Expedition (Lebanese University – DGAMS) has been working on the site of Cyrrhus. The main research topics are the study of the fortifications and the evolution of the town planning. In this paper the latest results on the polygonal fortification of the first phase of occupation are presented along with analysis of the development of the early town: its limits and town planning and its evolution in the Roman (64 BC with Pompey’s conquest), Byzantine and Islamic periods. The fortification in its actual state of preservation belongs, for the most part, to the Byzantine period. During the 6th century AD, under the reign of Justinian (527–65), the entire rampart was reconstructed, corroborated by several sources and inscriptions discovered on site. The study of the city wall uncovered some major interventions attributed to the medieval period. It is known that in 637, the city was conquered by the Arab army and named Qurus. It was re-occupied by the Byzantines in the early 11th century, and reconquered and dismantled in 1150 AD by Nur al-Din al Zengui.