The area around present-day Cairo, especially Memphis, which was the old capital of Egypt, had long been a focal point of Ancient Egypt due to its strategic location just upstream from the Nile Delta. However, the origins of the modern city are generally traced back to a series of settlements in the first millennium. Around the turn of the 4th century, as Memphis was continuing to decline in importance, the Romans established a fortress town along the east bank of the Nile. This fortress, known as Babylon, was the nucleus of the Roman and then the Byzantine city and is the oldest structure in the city today. It is also situated at the nucleus of the Coptic Orthodox community, which separated from the Roman and Byzantine churches in the late 4th century. Many of Cairo's oldest Coptic churches, including the Hanging Church, are located along the fortress walls in a section of the city known as Coptic Cairo.