"Gaul" was what Romans called a man of Celtic or Belgic race, no matter which part of the world he inhabited.

In 1864 he wrote an appeal to the current representatives of the "Celtic race", proposing Celtic festivals:

The Irish, who with the Scots comprised the Gaelic branch of the Celtic race, were a totally pastoral people.

Historical characteristics of the Celtic race (1885)

The university was later occupied by the Druids, the priest-magicians of the Celtic race.

One consequence was to result in sophisticated theories about Celtic races with Druid priests in Western Europe.

We were of the Celtic race, that tall people famed for their fierce blue eyes and fiercer passions.

The Celtic race!

The Gallic-Celtic-Iberian peoples, like many other tribes descended from the general "Celtic" race, put up an obstinate fight against Roman hegemony.

Napier was reluctant to include Caithness, which he regarded as '"not inhabited by the Celtic race".