The agglomeration of Plougasnou was founded between 514 and 525. In all probability the name Plougasnou originates from the name of its founder Cathnou…..Plou-Cathnou, the tribe of Cathnou. This is a true Celtic name. One of the abbots of Landévennec, the fifth successor of Saint Gwenole, was also called Cathnou. After having founded a huge tribe in Plougasnou, Cathnou took the old Roman road which began in Plougasnou at the ruined Roman encampement of Primel and didn’t stop until he reached the foot of the Arrée mountains in the centre of Brittany. The oldest document which mentions Plougasnou is the Charter signed by Duchess Berthe of Brittany and her son Conan in 1039, which gives the parish of Plougasnou to Saint George’s Abbey in Rennes. At this time Plougasnou consisted mainly of prairies and a large forest where in the XVII century large rewards were being offered to anyone who could catch any of the wolves which were plaguing the area at that time. During the reformation of 1543 the names of the Manor houses in the area were documented and it can be seen that there were a large number of noble houses in this area at that time…around 170. Plougasnou’s church of St Peter dates from the XI century. Inside the Renaissance porch we can see the name of the architect of the steeple, Master Jean Taillanter and the date 1582 and we can also see the date of 1616 engraved on one of the pillars.
Just to the east of the village centre is the Oratoire de Notre-Dame de Lorette. This is a small oratory which is unique in Europe and was built in 1611 by Jeanne de Keredan. In the olden days unmarried girls would put a lock of their hair on the altar as an offering, in the hope of obtaining a good husband. When it was built it would have been set amongst the fields and would have been visible from far away. The particluarity of this small oratory is that it is built with a vaulted ceiling in the style of a Lycian tomb.