Cloister at Moissac (ca. 1100 AD, southern France)
Cloisters were a medieval kind of building that developed out of Greek and then Roman peristyles.
A cloister is a courtyard garden inside a building. Often people grew herbs or fruit or flowers in the garden. Around the sides of the courtyard there is a covered walkway, with a waist-high wall between you and the garden in the middle. On top of the waist-high wall, small columns hold up the roof of the walkway.
Cloister of Munster, in Bonn, Germany
Christian monks built this cloister in the time of Friedrich Barbarossa). Munster means"monastery", and the town was named after this church and its cloister, where the monks lived. Cloister means a closed space, and some cloisters were enclosed so that nuns and monks could get some fresh air and have a garden without anyone seeing them or distracting them from their prayers. But other cloisters were just private courtyards, where people could hang out without danger of being attacked by enemies.
The first medieval cloisters, like early Islamic mosques, often re-used small columns from Roman buildings, to show how Christianity had beaten the Roman gods (and to save money). A little later on, cloisters used Romanesque arches; later on people began to build Gothic style cloisters. But by the time of the Renaissance, life in Europe wasn't so dangerous anymore, and cloisters went out of fashion. Instead people designed bigger, more open, and less protected gardens.