The western society in the early Middle Ages was impoverished and relatively underdeveloped compared to the Byzantine or Muslim lands. Not much monumental architecture survives from that period because later, more prosperous generations replaced the buildings. Aside from liturgical objects and manuscripts, there is little from before 1100 that would impress the ordinary modern observer. In the modern popular imagination, the 'real Middle Ages' corresponds to what historians call the central Middle Ages, a period that fiction writers and film makers love for its crusades, knights in armour, tournaments, stone castles, cathedrals, stained glass windows, monasteries, illustrated manuscripts, heretics, inquisitors and universities. In modern experience, migration is one response to population growth, but internal economic growth is another. But sometimes the forces retreated or paused in the face of the consciousness of belonging to something larger than one's region or kingdom, of belonging to the Christian people or western Christendom.