Carlysle's Mill was the Last Holdings of the Family Carlysle located in Eel's End in Riverside/South Quarter. At some point it became a Heritage Site. It was constructed long ago, but the exact date has worn away and is forgotten. In present times the abandoned mill became Erin's hideout; Erin's Mill.
The Carlysle's were a family in Thief II: The Metal Age. They owned Castle Carlysle in Dayport. Lord Carlysle was invited to Karras party at Angelwatch. It would seem that in the new Thief's history the family has since fallen and lost everything.