The kingdom of Strathclyde was focused on the Clyde valley and ruled by a Brittonic-speaking dynasty. Historians have traditionally argued that the kingdom expanded southwards in the early tenth century, with the result that there was a revival of Brittonic language. Several scholars have recently challenged this interpretation, but in this article I defend the view that Strathclyde expanded southwards, and I propose a new model for the process. I argue that the kings of Strathclyde took submissions from the local nobility, who included Northumbrian and Gaelic-Scandinavian magnates. This accounts for the multicultural nature of the kingdom in its heyday.