Romanesque is the name given to the style of art and architecture in the 11th and 12th centuries. Romanesque means "Romanlike." And the monasteries and churches built in this era are very Roman like. Barrel and groin vaulting constructed with brick or small brick like blocks of stone made up the fire proof roofs of southern French monasteries. While their piers were still making wooden ceilings. These types of vaulting were taken from the Roman style. The purpose was still the same but the technique had changed because now concrete technology had been lost. But the church aisles were still flanked by the Roman arch and high columns.
The Romanesque period was the time of Churches built for pilgrimage. These churches would house the relics of saints and their architects would build extra space in the nave and aisles to accommodate the pilgrims. The churches became a tourist attraction basically. And since cities were rising up every where. The construction of churches dedicated to certain saints housing their relics provided economic growth for the towns. As well as funds to the church itself which would allow for more construction of more churches. Which would allow the process to continue. Allowing for even more trial and error happenings to occur in which the medieval architects could perfect this new meshed style of building. This style and fad of building monolithic churches with thick walls, high ceilings, and scaling towers.
Even the art with the church had to stand the test of time just like it's thick walls. Stone carvings were put in place to not only help beautify the church but to reach out to the lay people within the cities. In the past the church had been something small met to serve just the clergy but with the rise of towns and pilgrimage routes. The church not only needed to make accommodations by building bigger but also by building for the illiterate. Many at the time could not read and by story telling through stone carving and sculpture they could learn Christian stories.
Paintings were still used to decorate the vaulted ceilings and many murals and frescoes still exist from this era but it was the revival of stone sculpture that was so Romanesque.
The arches. The stone vaults. The thick walls. The high ceilings. The large aisles. The stone sculptures. The huge buildings made for worship. And the relics in place to promote travel and economic growth from city to city. All define the Romanesque period.