At the heart of the modern city of Plovdiv rests the Old Town. Surrounded by Roman Walls, full of important monuments is one of the most important sight-seeing places in the whole Bulgaria. Here the visitor may explore and admire the Ancient Theater (built in the years of Roman Emperor Traianos), the Roman Agora and the Aqua duct (water reservoir). Remains of the Ottoman Empire may also be found, like the Clock-Tower and plenty of Muslim Mosques. Many Byzantine Christian churches are also scattered all around as well, with the one of Saint Constantine and Helena being the oldest. Besides all these monuments, the visitor should explore around the paved narrow streets of the Old Town and admire the well preserved mansions that travel you back to the past so vividly!