Architecture

One of the easiest ways to track the changing needs and temperaments of a time period is through the architecture. The middles ages are broken into several art periods. The early period is characterized by Byzantine and Islamic in the East, and a synthesis of late antiquity with northern traditions or the so-called barbarian invaders. With the rise of the church's influence, cathedrals and monasteries develop a style called Romanesque. These focus primarily in the 11th and 12th centuries and  the term itself is a fairly recent innovation. Previously these buildings and sculptures were considered an early phase of Gothic, but are now regarded as a separate school of architecture. The late middle ages saw the rise of Gothic art, beginning first in France in the late 12th century then spreading out with distinctive regional differences to the basic style.

The other major form of architecture during the middle ages took the form of castles and manor houses. After the fall of Rome most of Europe went through a violent age of power struggles. Many retreated behind high walls and thick fortifications. As kingdoms were created and things became more peaceful, villages became cities and castles became palaces. 

Check the links for some sites that list famous castles and cathedrals.