Ras (Serbian Cyrillic: Рас; Latin: Arsa), known in modern Serbian historiography as Stari Ras (Serbian Cyrillic: Стари Рас, "Old Ras"), is a medieval fortress located in the vicinity of former market-place of Staro Trgovište, some 11 km west of modern-day city of Novi Pazar in Serbia.

Old Ras was one of the first capitals of the medieval Serbian state of Raška, and the most important one for quite a long period of time. Located in today's region of Raška, the city was positioned in the center of the early medieval state. Its favorable position in the area known as Old Serbia, along the Raška gorge, on the crossroads and trading routes between neighbouring regions of Zeta and Bosnia in the west and Kosovo in the south, added to its importance as a city.

Today the fortress of Arsa lies in mostly unenclosed and unprotected ruins. However, there are plans for future reconstruction of the site. In the close vicinity of Arsa there is impressive group of medieval monuments consisting of fortresses, old market-places, churches and monasteries. Serbian medieval Monastery of Sopoćani near Arsa is a reminder of the contacts between Western world and the Byzantine world. The site of Stari Ras, in combination with the nearby Monastery of Sopoćani, is already a UNESCO World Heritage Site, and Stari Ras monastery (12th century) is being reconstructed and it too may be included on the UNESCO World Heritage List with the site. Stari Ras and Sopoćani World Heritage site is not far from another UNESCO World Heritage Site of Serbia, the magnificent medieval monastery and churches of Studenica. The sixth century Church of Saint Apostles Peter and Paul is one of the oldest early medieval churches in Serbia.

Stari Ras was declared Monument of Culture of Exceptional Importance in 1990, and it is protected by Republic of Serbia.