Horseshoe Arch (San Juan Banos)
Because Spain was part of the Roman Empire, at that time Spanish art looked a lot like other Roman art. It's not exactly the same - each province had its own way of doing things. Roman period Spanish art is usually stronger-looking and more forceful than art from other parts of the empire.
After the fall of Rome, when the Visigoths took over in Spain, there was less contact between Spain and the rest of the northern Mediterranean. Spanish artists became interested in the shapes of vines and flowers growing wild, and then they carved people and animals in the same twisted, crazy poses that they had used for the plants. Artists in Spain also learned some new styles from North African artists, who were influenced by the Byzantine Empire. One example is the horseshoe arch.
The Alhambra in Grenada
In the 700s AD, when the Moors conquered Spain, most Spanish artists worked in the Islamic style. They continued to use horseshoe arches, and also stopped showing people in favor of abstract designs because of Islamic and Byzantine iconoclasm. Spanish artists were particularly interested in using light and shadow to create art.
In the northern parts of Spain, where the rulers were still Christians, Islamic styles mixed with Christian styles to create a kind of art that was called Mudejar (moo-day-JAR).
James I of Aragon's Knights Marching to Fight the Moors,
fresco, 13th century.