Although there is much talk that the Irish have been under the yoke of English tyranny for over 800 years, the fact is that this did not really and seriously come about until the time of Henry the VIII. It is true that, since Strongbow's "invasion" in the 12th century, there had been a settlement of Anglo-Norman descendants who got along quite well with the Irish population. They existed to a large part within the "Pale" and its environs and, beyond the Pale had inter-married and flourished in the Irish community (the de Burgos had become Bourkes and Burkes). In many ways they had become "more Irish than the Irish") in spite of English Law. They had adjusted to the Brehon Law of the Irish - finding it more accomodating to their needs at that time.
Since the Donnellans were principally located in Galway and Roscommon, they still payed their allegiance to the O'Kellys, King of the Hy Many, and accepted leaders in O'Kelly's Country for hundreds of year. Their place within this community was established as the "Cathmhaol" or Battle Champion of the Clan. This position was a traditional one dating back over 1000 years. Their principal home or "baile" was at Ballydonnellan Castle in the County Galway.
The king (O'Kelly) commonly kept in his retinue a champion, or chief fighting man, to answer challenges to single combat. In the Ui Maine, this honor was bestowed on the Clann Breasail (O'Donnellan chiefs) as hereditary keepers of arms. The duties of the family and their adherents was solely concerned with the martial arts. The first duty was to answer any challenge put to a king by an outside party. They were also obligated to equip, train and and command forces during battle. A challenge could involve mano-a-mano combat between two champions or full-scale war between two armies.
In ancient times, the warriors wore little or no armor, often going into battle wearing only a torque, or gold band, around the neck. The protection of armor was considered unmanly and disgraceful by the ancient Irish. This quickly changed, however, after the invasions by the Danes and later the raids by the Anglo-Normans. The battle champions were considered ollaves, or expert teachers, and their position in the Clan was justly respected.
According to O'Donovan, in The Tribes & Customs of Hy Many, 18 Donnellans were killed at the Battle of Turlaghvohan near Tuam fought between Hugh O'Conor, commonly called Hugh Iongagh Varna and Hugh O'Rorke, King of Brefinee. Other than O'Donovan, I have found no further mention of when or where exactly this Battle took place. In may be indicative, however, of when the Sept laid down their arms and adopted the motto "Greater than all Violence".
To date, this is all the verifiable evidence I have through about 1500 AD. Now the documentation increasingly becomes more abundant and will be published to this site in the form of pedigrees and supporting documentation.