Historians have identified two main types of medieval cathedrals, usually classified as Romanesque and Gothic. Cathedrals in the Romanesque style were generally constructed between about 800 and 1200 CE. Gothic cathedrals were generally constructed between about 1200 and 1500 CE. Most historians believe that the Romanesque style of architectural construction borrowed heavily from the architectural conventions of both Byzantium and the Roman Empire. Medieval cathedrals constructed in the Gothic style typically included more decorative embellishments, and usually incorporated architectural advancements that allowed for larger windows and higher ceilings.
The main characteristics of Romanesque architecture in the Middle Ages typically include very thick, strong stone walls, small windows, and large pillars meant to hold up the cathedral's roof. Architects at this time used numerous stone vaults in building their cathedrals, probably because they believed this architectural feature could limit fire damage in the event of a blaze. Arches are also found in many Romanesque-style medieval cathedrals. Regular arches were often used for architectural support, but blind arches, as they are called, were often built into the walls of these cathedrals as a decorative feature. In addition, many cathedrals built in the Romanesque style were cross-shaped in their construction, sported more than one tall tower, and often had aisles running down the sides of the interior along the nave.
Gothic cathedrals are usually larger and better lit than Romanesque-style medieval cathedrals, because these structures were able to incorporate architectural advancements that allowed for thinner, lighter walls and bigger windows. Most historians of architecture credit the invention of the flying buttress with the advent of Gothic architectural styles. This feature allowed architects of the time to support the heavy stone roof of the cathedral from the outside, so that walls and interior pillars did not have to be as thick to prevent the cathedral's collapse.
Most medieval cathedrals with large, stained-glass windows are done in the Gothic style. Gothic cathedrals typically also have much higher ceilings, though they still normally incorporate arches, vaults, and pillars. Gothic-style cathedrals are typically much more ornately decorated, especially on the outside. Gargoyles, sculpted religious scenes, statues of religious figures, and even small humorous sculptures can appear on Gothic-style cathedrals. These cathedrals were often constructed with interior aisles along the sides of the nave, and many also contained small private chapels and shrines constructed off the sides of the nave.
Most historians believe that medieval cathedrals were constructed by groups of unskilled laborers usually instructed by well-trained and knowledgeable artisans. The construction of a cathedral was usually ordered by the bishop of the dioceses, who typically collected donations from the community, and especially from those about to die, to fund the project. Historians believe that large medieval cathedrals were probably considered necessary to accommodate the many religious pilgrims who traveled through Europe at the time, passing through various communities in order to pay homage at important Christian shrines.