Stay on the same sidewalk for about 250m (after the castle). You can see the layers of the old Roman road. Take on the right the path to Trégouët Abbey, and climb the hill up to the Temple.
On this hill, the largest Gallo Roman sanctuary of Brittany stands.
Created ex-nihilo, this monument appears as a tool to serve the integration of the local populations and shows the dedication of the Coriosolites city to the Empire. Its construction, based on the size and the cost, was in two stages and on a few decades between the end of the 1st and the beginning of the 2nd century AD. The Romano-Celtic building, facing east, is organised around a vast sacred courtyard covering 5,000m² (108m x 98m). and is surrounded by three raised porticoes. It is said to be Romano-Celtic since it uses, in its architecture, a polygonal cella (most sacred area of the sanctuary) in Celtic tradition, associated to the Greek system with three porticoes, the whole linked with the Etrusco-Italic constructions through its frontality. The columns are in the Tuscan style, very puridied Roman architectural order.
One entered the sanctuary through the vestibules which allowed to host, control and guide the pilgrims. The sacred area could hold around 5,000 people. The processions and calls of the Emperor representatives took place under the porticoes.
The octogonal cella, (tower originally 22.50m heigh) of which four walls still remain, was the most sacred area of the sanctuary, reserved to the sacerdos (priests) and the elite. The cella housed the tutelar deity's statue, Mars Mullo. The pilgrims couldn't access this area.
To pray to the god, they turned in the adjoining gallery and left their offerings to the God in a small exedra.
The sanctuary was destroyed by fire, most likely between 275 and 290 AD. Voluntary fires caused during pillages by Saxon pirates going up the Rance River, or by peasants revolts against imperial power and social order. Many a building, public or private, walls or enclosures, of the area has been built with the stones from these ruins.
An interpretative itinerary in free access shows you the life of the sanctuary.
Slip into Gaius' mind, our mascotte, and let yourself be lead into the pilgrim's ceremony!
Go around the site and retrace your steps to CORIOSOLIS.

Cross and go on the Mairie parvis. On the left, the Jardin des Antiques offers a perspective on the ancient Roman road and Monterfil Gallo-Roman commercial district.
A Gallo-Roman city is also an important economic power and with its 5,000 inhabitants meant, for this eran an enormous market.
The food products are, for a large part, from the surrounding countryside, and by faraway imports from Italy or Spain such as wine, oil... Some crafted goods are also made here, but a lot of them come from trading with other Gaulish cities or farther away regions of the Empire.
All the discovered objetcs found through search testify to this intense economical life in which currency was the necessary medium of exchange for transactions.
The most important road of the Ancient city crosses the district from west to east ends in the forum. It is lined, north, by a great commercial building with activities and warehouse, caracterised by an imposing portal and, south, by three buildings housing shops, a meeting place (private basilica) and, at the back, the shopkeepers and craftmen's houses. Go down the steps and close your eyes, imagine yourself as a character from the Ancient times walking down this street full of shops and noises.
If you stop now, the itinerary is 2km long, the Coriosolites' sanctuary, called Temps de Mars (Mars Temple) is accessible by car.

Once in Rue de l'Arguenon, turn left, then right in Rue du Montafilan, 1st on the left and then again left to the church. The entry to the church is on the parking lot side (public lavatory).

According to Roman Law, it is forbiden, for hygiens reasons as well as for the sacred nature of the urban territory, to bury people inside the cities. Necropolis to bury or incinerate, "out of the walls", had funerary monuments (mausoleums, stelae). Inside the church, at the basis of a pillar on the south side of the church, one can find a stela erected, to his mother's memory, by a Roman citizen. This Carthaginian woman, Siligia Namgidde, left her country to be with her son in the Coriosolites' city. She died there, age 65.

There used to be little industries in Plélan, and the granite quarries poorly worked because of a relative isolation.
In the 1930's, Plélan, chef lieu de canton (administrative centre of a groupe of villages), had 980 souls.
After the war, the surroundings of the streets, the village centre and the national road are built, changing the village into a street-city.
The village-centre then had 7 bars, 2 bakeries, 2 butchers, 1 cobbler, 1 saddler...
There are manly small shop owners and artisans. There are no entreprises, unlike Plancoët, because of a lack of roads and of port.
In front of the back of the church, the old "Hôtel des voyageurs" can be found, a hotel that had 5 rooms and of a sometimes subversive reputation.
300m from there to the South, at the bottom of the playging fields, used to be a train station for the lign Jugon-Dinan, taken apart in 1938/1939. The train had four 4 wagons (3 for goods/ 1 for travelers).
Plélan was a quiet village, its inhabitants united.
From the 1970's onward, the good situation of the village helps the installation of new inhabitants. Its when the mairie was built with the granite extracted South of the village.
Go around the building by the left and follow the street.

This modern building is situated on a history packed site.
On what to be only marshes, as the streets' toponymy tells us, were, on a mount, three crosses (which can be found at the graveyard later on).
These three crosses were moved for the construction, in 1941, by the German, who were in fact Austrians, of barracks meant to house Tirailleurs sénégalais (Senegalese infantry corps), brought down into slavery to clear the earth and plant over the moors.
After the war, this lugubrious place became a place for celebrations; the inhabitants of Plélan, taking on the habit, as reavenge on the past, to celebrate there the return of the war prisoners.
In 1953, the townhall decided to officialy build the village hall there by enlarging the existing building. Inaugurated three years later, it became renown in the area as so many weddings, bals, bingoes take place there.
Being out of standards, the village hall was torn down in 2009. A new village hall, more spacious is built next of des Garennes and, on these grounds in the centre of the village, between the schools, this cultural centre is built.