In 391, there is a reference to large dogs by Quintus Aurelius Symmachus, a Roman consul who got seven "canes Scotici" as a gift to be used for fighting lions and bears, and who wrote "all Rome viewed (them) with wonder".^[10] Scoti is a Latin name for the Gaels (ancient Irish).^[11] Dansey, the early 19th century translator of the first complete version of Arrian's work in English, On Coursing, suggested the Irish and Scottish "greyhounds" were derived from the same ancestor, the vertragus, and had expanded with the Scoti from Ireland across the Western Isles and into what is today Scotland.^[12]

Wolfhounds were used as hunting dogs by the Gaels, who called them Cú Faoil^[13][14] (Irish: Cú Faoil [ˌkuː ˈfˠiːlʲ], composed of the elements "hound"^[15] and "wolf",^[16] i.e. "wolfhound"). Dogs are mentioned as cú in Irish laws and literature dating from the sixth century or, in the case of the Sagas, from the old Irish period, AD 600–900. Cú Chulainn, a mythical warrior whose name means "hound of Culann", is supposed to have gained this name as a child when he slew the ferocious guard dog of Culann. As recompense he offered himself as a replacement.^[14]

In discussing the systematic evidence of historic dog sizes in Ireland, the Irish zooarchaeologist Finbar McCormick stressed that no dogs of Irish Wolfhound size are known from sites of the Iron Age period of 1000 BC through to the early Christian period to 1200 AD. On the basis of the historic dog bones available, dogs of current Irish Wolfhound size seem to be a relatively modern development: "it must be concluded that the dog of Cú Chulainn was no larger than an Alsatian and not the calf-sized beast of the popular imagination".^[17]

In his Historie of Ireland, written in 1571, Edmund Campion gives a description of the hounds used for hunting wolves in the Dublin and Wicklow mountains. He says: "They (the Irish) are not without wolves and greyhounds to hunt them, bigger of bone and limb than a colt". Due to their popularity overseas many were exported to European royal houses leaving numbers in Ireland depleted. This led to a declaration by Oliver Cromwell being published in Kilkenny on 27 April 1652 to ensure that sufficient numbers remained to control the wolf population.^[18][19]

References to the Irish Wolfhound in the 18th century tell of its great size, strength and greyhound shape as well as its scarcity. Writing in 1790, Thomas Bewick described it as the largest and most beautiful of the dog kind; about 36 inches high, generally of a white or cinnamon colour, somewhat like the Greyhound but more robust. He said that their aspect was mild, disposition peaceful, and strength so great that in combat the Mastiff or Bulldog was far from being an equal to them.^[20]

The last known wolf in Ireland was killed in County Carlow in 1786.^[20][21][22] It is thought to have been killed at Myshall, on the slopes of Mount Leinster, by a pack of wolfdogs kept by a Mr Watson of Ballydarton. The wolfhounds that remained in the hands of a few families, who were mainly descendants of the old Irish chieftains, were now symbols of status rather than used as hunters, and these were said to be the last of their race.^[20]

Thomas Pennant (1726–1798) reported that he could find no more than three wolfdogs when he visited Ireland. At the 1836 meeting of the Geological Society of Dublin, John Scouler presented a paper titled "Notices of Animals which have disappeared from Ireland", including mention of the wolfdog.^[23]

Captain George Augustus Graham (1833–1909), of Rednock House, Dursley, Gloucestershire, was responsible for reviving the Irish wolfhound breed. He stated that he could not find the breed "in its original integrity" to work with: