During the 13th century, when the Athollmen were raised, it was usually for local defensive duty or for raids on neighboring lands. However, when called, they would muster and support the Earl of Atholl's undertakings outside the district.

The first earl was Earl Madach, the son of Maelmare, the youngest brother of King Malcolm Canmore. The earldom was established by King Edgar prior to 1106 for Madoch, his uncle's son. On Madach's death the earldom reverted to the Crown and to keep the earldom in the family, it was given to Malcolm, the son of King Edgar's half-brother Malcolm. This Malcolm (the second celtic earl of Atholl) married Hextilda, a granddaughter of King Donald (Ban) III and their eldest son was Henry. Earl Malcolm witnessed the confirmation of the Foundation Charter of Scone by King Malcolm IV in 1165. Henry was the third and last celtic earl of Atholl (1198-1222).

King Donald (Bane) III had been deposed and blinded in 1097 prior to King Edgar (1097-1107) fourth son of Malcolm Canmore and Saint Margaret taking the throne. This competition for the throne resulted from the competing family claims between celtic tanistry and Norman primogeniture after Malcolm Canmore's death in 1093. The MacWilliam claimants were descendants of King Duncan II's second son William. King Duncan II was the eldest son from Malcolm Canmore's first marriage and was killed by King Donald (Bane) III (Malcolm Canmore's brother) in 1094.

Earl Henry raised a force of Athollmen in 1211 and was one of the commanders of the expedition into the earldom of Ross against Godfrey (Guthred) MacDonald MacWilliam. Godfrey was the great-grandson of Duncan II and was a claimant to the Scottish throne. He was in rebellion against King William I (grandson of King David (1124-1153) youngest son of Malcolm Canmore). Godfrey was slain in 1212. When King William I (1165-1214) died in December 1214, Earl Henry was present at the coronation of William's son, King Alexander II at Scone soon after. During the 35 year reign of Alexander II (1214-1249) and the 37 year reign of his son Alexander III (1249-1286), there were few serious conflicts with England and there was an unprecedented era of peace between the two countries.

Earl Henry had two sons, Constantine (who predeceased him) and Conan. When Henry died around 1222, the earldom passed through his first son's daughters successively to their respective husbands. The youngest daughter, Fernelith married Sir David Hastings and in her right he became the seventh Earl of Atholl. Their grandson David became the 9th Earl. Known as the Crusader Earl, he took the cross in 1268 and raised a force of Athollmen and joined King Louis IX's second Crusade against the infidels in 1270. Unfortunately, he and most of his men died during the siege of Tunis in August 1270. Their son John the 10th earl was a steadfast adherent of King Robert the Bruce and was at his coronation in 1306. Unfortunately he was captured by the English, condemned to death and hanged on November 7, 1306.

Despite this setback, the family continued to prosper and on February 26, 1312, David the 11th Earl of Atholl was invested with the office of High Constable of Scotland by King Robert the Bruce. Then through his treachery, the family lost all in Scotland. On the night of June 23rd, the 11th Earl led his men in an attack on the Scots' supply depot at Cambuskenneth Abbey and killed the defenders. The next day King Robert's army destroyed the English army in the Battle of Bannockburn. After the Scottish victory, the Earl was deprived of his office of High Constable, the earldom reverted back to the Crown and all of his estates in Scotland were lost. King Edward II amply rewarded him with estates in England for his treachery and he later served as King Edward III's Governor of Scotland, but his descendants no longer considered Scotland their home.

Earl Henry's second son, Conan, is the founder of the "de Atholia" line from which our clan chiefs descend. As Henry's illegitimate son, Conan could not inherit the earldom, but he did receive the lands of Glenerochy that were not tied to the earldom on his father's death. Conan's son was known as Ewen FitzConan of Glenerochy. After Conan's death, Ewen confirmed a grant made by his father in 1216 to the abbey of Coupar Angus for the provision of firewood to the abbey. Conan also granted a charter to the abbey of Lindoris in 1220 which was witnessed by Ewen. Ewen married Mary, the daughter and co-heiress of Convalt, Lord of Tulliebardine. In 1282, a wadset or mortgage was issued as security for the twenty merks advanced to Ewen by the monks of Coupar Angus on his wood at Killbroachache.

After Conan, the next three generations (Ewen, Angus and Andrew) married well and brought more lands to the family. Little is known of Ewen's son Angus, so he may have died soon after fathering his son, Andrew de Atholia (Conan's great grandson). Certainly, Ewen would have been present to witness the departure of the crusader 9th earl of Atholl and his men for France in 1269. When Andrew became head of the family after 1282, his estates were held by either Crown or church charters. Andrew's son Duncan de Atholia is recognized as the first chief of the Clan Donnachaidh.

Through Duncan's marriage to the daughter of Malcolm, 5th earl of Lennox, he acquired the lands of Rannoch and was also known as the Lord of Rannoch. His eldest son and successor was Robert de Atholia. Robert's younger brothers led the clan on the famous "Raid of Angus" in 1392.

Thus the fortunes of the descendants of Henry Earl of Atholl can be traced as they rose and fell over the course of the following centuries.

References:
Cowan, Samuel, "Three Celtic Earldoms", 1909, pp.13-15.
Dixon, John H, "Pitlochry Past and Present", 1925, p. 107.
National Trust for Scotland, "Bannockburn", 1987, p. 27.
Paton, Sir Noel, "Descendants of Conan of Glenerochy", 1873, pp. 2-4.
Rait, Robert S., "The Making of Scotland", 1929, pp. 52.
Robertson, James A., "The Earldom of Atholl", 1860, pp. 15-16, 18.