Archaeological excavations show that the site of Romainmôtier was inhabited from the dawn of the Christian era. Remnants of building foundations have been uncovered close to the Nozon River.
The vestiges of the first monastery date back to the middle of the 5th century.
The first church is thought to have been built by monks from the French Jura, including Romanus. The site fulfilled their wish for isolation while being close to the thoroughfares crossing the Jura. Saint Romanus of Condat is considered one of the fathers of the Jura. He actively spread the Christian faith in the region.
At this time, Romainmôtier was part of the Kingdom of Burgundy. In 515 AD, King Sigismund founded the Abbey of Saint Maurice at Agaunum (in Valais) and invited monks from the Jura to become part of the community there.