Paul-Yves Pezron was a seventeenth-century priest from Brittany

Brittany

Brittany is a cultural and administrative region in the north-west of France. Previously a kingdom and then a duchy, Brittany was united to the Kingdom of France in 1532 as a province. Brittany has also been referred to as Less, Lesser or Little Britain...

, best known for his 1703 publication of a study on the common origin of the Bretons

Breton people

The Bretons are an ethnic group located in the region of Brittany in France. They trace much of their heritage to groups of Brythonic speakers who emigrated from southwestern Great Britain in waves from the 3rd to 6th century into the Armorican peninsula, subsequently named Brittany after them.The...

 and the Welsh

Welsh people

The Welsh people are an ethnic group and nation associated with Wales and the Welsh language.John Davies argues that the origin of the "Welsh nation" can be traced to the late 4th and early 5th centuries, following the Roman departure from Britain, although Brythonic Celtic languages seem to have...

, Antiquité de la nation, et de langue des celtes.

In his time, he was known in France as a chronologist. Pezron traced Welsh and Breton origins to the Celt

Celt

The Celts were a diverse group of tribal societies in Iron Age and Roman-era Europe who spoke Celtic languages.The earliest archaeological culture commonly accepted as Celtic, or rather Proto-Celtic, was the central European Hallstatt culture , named for the rich grave finds in Hallstatt, Austria....

s of ancient writers, and traced the Celts further to eponymous hero-patriarchs from Gaul

Gaul

Gaul was a region of Western Europe during the Iron Age and Roman era, encompassing present day France, Luxembourg and Belgium, most of Switzerland, the western part of Northern Italy, as well as the parts of the Netherlands and Germany on the left bank of the Rhine. The Gauls were the speakers of...

 to Galatia

Galatia

Ancient Galatia was an area in the highlands of central Anatolia in modern Turkey. Galatia was named for the immigrant Gauls from Thrace , who settled here and became its ruling caste in the 3rd century BC, following the Gallic invasion of the Balkans in 279 BC. It has been called the "Gallia" of...

. Pezron believed the Welsh language

Welsh language

Welsh is a member of the Brythonic branch of the Celtic languages spoken natively in Wales, by some along the Welsh border in England, and in Y Wladfa...

came from a mother tongue called Celtick, a language that was only a theory to other authors. Pezron's fairly unscientific book was popular and reprinted until the early nineteenth century.