Tiruchirappalli, also called Tiruchi or Trichy, is a city in the Indian state of Tamil Nadu and the administrative headquarters of Tiruchirappalli District. It is the fourth largest municipal corporation and the fourth largest urban agglomeration in the state. Located 322 kilometres south of Chennai and 379 kilometres north of Kanyakumari, Tiruchirappalli sits almost at the geographic centre of the state. Tiruchirappalli is one of the oldest inhabited cities in Tamil Nadu; its earliest settlements date back to the second millennium BC. Uraiyur, the capital of the Early Cholas for 600 years from the 3rd century BC onwards, is a suburb of present-day Tiruchirappalli. The city is referred to as Orthoura by the historian Ptolemy in his 2nd-century work Geography. The world's oldest surviving dam, the Kallanai about 18 kilometres from Uraiyur, was built across the Kaveri River by Karikala Chola in the 2nd century AD. Trichy may have been a capital of the early Cholas in the 3rd century BC. It passed through the hands of the Pallavas, medieval Cholas, Pandyas, Delhi Sultanate and Vijayanagars before the Madurai Nayaks brought it to prominence, making it a capital in the 17th century and building its famous Rock Fort Temple. Under British control, it became an important railway hub known as Trichinopoly.