The Maxwell's actually obtained Calderwood Castle through marriage, and rebuilt it. It is known that there was some sort of building on the land prior to 1246, which is when the Maxwell's took ownership. When the Maxwell's obtained the land, they then built Calderwood Castle in its last known form. My ancestors are Calderwood's from this area and all information I have found (including speaking to the local historian) states that the Calderwood surname almost certainly originates from this area.