The Sack of Mournhold was an event that occurred during the last year of the First Era. It was caused by the Dunmer witch Turala Skeffington, as she believed the current Duke of Mournhold was responsible for the death of her daughter, Bosriel.
An Orc hunting party had wiped out the settlement of the Skeffington Coven, along with the five-month old daughter of Turala Skeffington. Turala was lead to believe that Indoril Brindisi Dorom (who was the former lover of Turala and father of Bosriel, as well as being the Duke of Mournhold), was responsible. She grew so enraged with him that she summoned Mehrunes Dagon to destroy Mournhold.
The Duke's forces held out for four days, until Mehrunes Dagon made a strong attack on Castle Mournhold. The castle was said to be: A gout of ever-erupting flame, and that the only thing stopping the fires from spreading was wet, sputtering blood of [Mournhold's] people. Sotha Sil and Almalexia defeated Mehrunes Dagon, with Almalexia overseeing the rebuilding effort. This battle is the reason for Almalexia residing in Mournhold.