Horses and Ponies from the Celtic Regions: The Galician Pony

The Galician Pony is built much like a horse, rather than a pony. They originate in northwestern Spain, in a region called Galicia. Their ancestors are a mix between Celtic and Roman horses. Historically, they weren't just used for riding. Their manes, tails, and forelocks were used to make hair brushes. They were also bred for meat. Today, they still live semi-feral. Each year, there is a festival where all the herds are rounded up to trim their manes, brand them, sell a few, and then turn them back into the wild Galician mountains.
The height ranges from 12.2hh-13.2hh. Their colors include various shades of Bay, Chestnut, and Black - in addition to exhibiting Grey and Tobiano. This breed is also known to amble, but not all individuals inherit the gene.

Resources:
http://www.theequinest.com/breeds/galician-pony/
https://www.horsebreedspictures.com/galician-horse.asp
http://www.second-opinion-doc.com/galician-pony-breed.html

Notes on Cantabria
There are three regions in northwestern Spain: Galicia being the furthest west; Asturia is next; and Cantabria being on the east side of Asturia. I researched if there was a native horse or pony breed of Cantabria that was old enough to come in contact with the Celts, but found none.