Lanark Castle was the origin and heart of what later became the royal burgh of Lanark, Scotland. The town grew up outside the castle walls. Long since demolished, the castle lay high on the east bank of the River Clyde, near the confluence with the Mouse Water. As a key strategic high point over the Clyde Valley, the Romans built a fortification on what is still known as Castle Hill, south west of the modern town centre. Other fortifications were built on the site after the Romans brief occupation of southern Scotland came to an end.