House Blacktower of Karthmere is an extinct noble house of the Borderlands. Their sigil was a black tower on a crimson field.

Their seat was the castle of Karthmere, which was granted to them by Asterion the Black as a reward for their service in the extinction of House Karth, the original occupants of Karthmere. However, the Blacktowers eventually became extinct, and the castle was passed on to House Valennis.