Romanesque architecture is a style of medieval Europe featured with semi-circular arches. There are many opinions about the beginning date of this style.

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The story of Romanesque
Romanesque architecture was the first distinctive style to spread across Europe since the Roman Empire. After the decline of Rome, Roman constructing methods were still used in Western Europe: Merovingian, Carolingian, and Ottonian architects went on building large stone constructions such as monastery churches, and palaces.

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In the northern countries, Roman building styles and techniques had never been adopted, were used just for official buildings, while in Scandinavia they were completely unknown. Although the round arch was still used, the engineering skills that obliged to vault large spaces and build large domes were slightly changing. Stylistic continuity was interrupted.

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Romanesque Architecture also spread at the same time in the north of Italy, France and the Iberian Peninsula. The style, named First Romanesque or Lombard Romanesque features thick walls, lack of sculpture, and the importance of rhythmic ornamental arches.
Main Characteristics
Romanesque churches usually included semicircular arches as windows, doors, and arcades; barrel or vaults to sustain the roof of the nave; piers and walls, with not so many windows, to contain the thrust of the vaults. Aside aisles are used with galleries above them with a large tower over the crossing of nave and transept. Smaller towers were built at the church’s western end.
French churches followed the scheme of the early Christian basilica plan, using radiating chapels to accommodate more priests. Around the sanctuary apse it could be found ambulatories for visiting pilgrims, and large transepts between the sanctuary and nave.

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Features
Romanesque Architecture has the following features:
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- Walls were solid to support the weight of the stones.
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- The use of the Roman arch was important to sustain the overall weight.
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- The windows had to be small to keep the strength of the walls strong.
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- The Vaults were the most important structural elements of Romanesque architecture, enabling the construction of stone roofs. There were many types of vaults:
- Barrel or Tunnel Vaults: consisted of a semicircular section similar to a tunnel.
- Groin Vaults: it is a vault produced by the intersection, at right angles of two barrel vaults.
- Ribbed Vaults: essentially two barrel vaults meeting at a right angle.

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Sculptural Decoration
One way in which Romanesque architects used to decorate their exteriors was with sculptures, especially over the entrance of the church. These round, decorated portals, called tympanum, became quite popular in Romanesque architecture.

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Info source:
http://study.com/academy/lesson/romanesque-architecture-characteristics-examples-history.html
http://www.britannica.com/art/Romanesque-architecture
http://www.medieval-life-and-times.info/medieval-art/characteristics-romanesque-architecture.htm
https://www.nanocathedral.eu/index.php/pisa-cathedral/
https://en.wikipedia.org/wiki/San_Liberatore_a_Maiella
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