The style of architecture in which Saint Sophia was built takes its name from the ancient name of the city and is called Byzantine. It is marked by domes and cupolas, and especially by long rows of round arches resting upon columns, and other arches resting upon them, making arcades, or corridors, one above another. It is always richly ornamented with gold and glowing colors.

One glance at the church of Saint Mark in Venice would show that this, too, is of Byzantine architecture, for it has so many domes and cupolas and arcades. During the century and a half that the Venetians were building it, every vessel that came to Venice from the East was required to bring pillars and marbles for the church. It is no wonder that the principal front has five hundred columns. Over the centre of the vestibule are the famous "horses of Saint Mark." When was for a time in the hands of the crusaders, they took these horses from the hippodrome and brought them to Venice. Napoleon carried them to Paris, but in 1815 they were taken back. The interior of Saint Mark, like that of all Byzantine buildings, is rich and brilliant. The walls are lined with rare marbles, and the floor is made of tessellated, or checkered, mosaic work.

The Moors and Saracens built many mosques and palaces. The most renowned of these is the wonderful Alhambra in Spain, which was erected in the fourteenth and fifteenth centuries. Longfellow calls it an enchanted palace. Its courts and pavilions are marvelously beautiful. Some of its ceilings are inlaid with silver and ivory and mother of pearl and tortoise shell. Others, as well as its walls, are ornamented with most graceful stucco arabesques, or delicate tracings of plants and vines, half from nature and half conventional, but always exquisite. Here and there are quotations from the Koran; but the Arabic letters seem only a part of the ornamentation. The stucco was formerly brilliant with gold and color, and some portion of this still remains. Everywhere are columns and arches. One court is especially famous for its beauty; and it has been painted and described so many times that to thousands who have never been in Spain it is almost as familiar as their own houses. This is called the Court of the Lions, because within it is a fountain of marble and alabaster in the shape of twelve lions surrounding a basin. The Koran, as has been said, forbade Mohammedans to copy animal life. Nevertheless, here are the lions.

After the ninth century, a style of building became common which has received the name of Romanesque because it is somewhat like the old Roman fashion. The roof of the Romanesque church was vaulted, and therefore the walls had to be made thick and solid to support it. The number of windows was not large, and what there were gave little light because of the thickness of the wall. There were towers, but the building as a whole was rather low and wide, and even the towers could not give it grace. The church at Angoulême is Romanesque. It looks strong and sturdy, as if it belonged where it stands and meant to stay there, but it is not beautiful.

After the Romanesque style came the Gothic architecture; and this is generally the style meant when people speak of the architecture of the Middle Ages. Its special characteristic is a pointed rather than a rounded arch. Guesses without number have been made as to what suggested the pointed arch. They have ranged all the way from Noah's ark to the lines made by the crossing of the branches of trees planted in rows. Gothic churches, such as the cathedral at Cologne, have pointed arches at doors and windows, and the pillars are in clusters instead of standing separately, as in the Roman and Greek architecture. The roofs are vaulted. Their weight tends to push the walls outward, especially as these are high and full of windows. Instead, however, of thickening the walls, as in the Romanesque style, the architects made outside supports called flying buttresses. In the Gothic churches there are many slender pinnacles, and there is a vast amount of carving. The general effect is of richness and splendor, while the many perpendicular lines give a certain lightness and grace which no other style of architecture can produce. The Gothic church is usually built in the shape of a cross, with a spire or tower at the place where the long and the short arms of the cross intersect. In the plan, a  is the nave, b  the transept, and c  the choir. Within the choir was the chancel. The tower or towers rose at a. Here was hung the large bell, after being marked with its name and the date, and after being christened with water and anointed with oil. Sometimes in places near the coast a church tower was provided with a cresset, or iron basket in which a signal fire might be kindled. At first, the Gothic architecture was used for churches only; but later castles, bridges, palaces, and gates of cities were built in this style.