The Main South Line, sometimes referred to as part of the South Island Main Trunk Railway, is a railway line that runs north and south from Lyttelton in New Zealand through Christchurch and along the east coast of the South Island to Invercargill via Dunedin. It is one of the most important railway lines in New Zealand and was one of the first to be built, with construction commencing in the 1860s. At Christchurch, it connects with the Main North Line to Picton, the other part of the South Island Main Trunk.