The title and territory of the Earl of Ross had originally been held by the Chief of Clan Ross but had passed through an heiress to the Leslie or Lesley family in the early 15th century. However, Angus Og's grandson, Donald of Islay, Lord of the Isles married Mariota, Countess of Ross (Margaret Lesley) who was the heiress of the Leslie Earls of Ross and he later claimed the position of Earl of Ross through this marriage. In 1411, Donald secured Dingwall Castle which was the principal seat of the Earldom of Ross, after he had defeated the powerful Clan Mackay who were supporters of the Stewart confederacy at the Battle of Dingwall. This in turn resulted in the indecisive Battle of Harlaw on 24 July 1411 fought between Donald of Islay's forces and those of Robert Stewart, Duke of Albany. There may have been as many as 10,000 men in the army of Donald at the Battle of Harlaw, but he failed to inflict a decisive victory and withdrew back to the Western Highlands. In the aftermath, Albany was able to retake Dingwall and seize control of Easter Ross. By 1415 the Earldom of Ross was with Murdoch Stewart, Duke of Albany. Donald prepared for war and proclaimed himself "Lord of Ross". However, the Duke of Albany appointed his own son John Stewart, 2nd Earl of Buchan as the new Earl of Ross.