de Silos, Santo Domingo de Silos, Castile and León, Spain San Martín de Tours, Frómista, Castile and León, Spain The Basilica of San Isidoro, León, Castile and León, Spain San Vicente, Ávila, Castile and León, Spain Sant Climent de Taüll, Taüll, Catalonia, Spain The Cathedral of Zamora, Zamora, Castile and León, Spain Old Cathedral, Salamanca, Castile and León, Spain Lisbon Cathedral, Portugal Old Cathedral of Coimbra, Portugal Monastery of Rates, Póvoa de Varzim, Portugal Romanesque churches in Germany, Belgium and the Netherlands Influences Much of Germany, Belgium, and the Netherlands were united under Charlemagne who built a castle on the Valkhof, Nijmegen, the Netherlands, and the Palatine Chapel at Aachen. The power of individual bishops and the establishment of cathedrals and monasteries were focused initially in the south of Germany and the Rhineland. In the early 10th century Germany and Lombardy were united under Otto the Great, crowned in Charlemagne's church at Aachen. Consolidation under Frederick Barbarossa in the 12th century led to the establishment of towns, imperial palaces and churches of imperial patronage. Despite internal divisions and threats from Poland, Hungary and Denmark, Germany regained power and in the early 13th century Frederick II became Holy Roman Emperor of Germany, Sicily, Lombardy, Burgundy and Jerusalem. Southern Germany, the Rhineland and Belgium had abundant building stone. Saxony and Flanders had little stone, while large parts of the Netherlands and the river plains of northern Germany had none, so that brick was the main building material. Timber was abundant in Germany and Belgium. The rich fertile river valleys, particularly those of the Rhine and the Meuse, encouraged the growth of towns. The period dating from the 9th to the 13th century produced Romanesque churches. Several important Early Romanesque churches occur in Saxony at Hildesheim and Gernrode. Many of the most notable examples of Romanesque architecture occur around the Rhineland, with twelve churches of this period in the city of Cologne. Characteristics The most distinctive characteristic of large Romanesque churches is the prevalence of apses at both ends of the church, as on 9th-century Plan of St. Gall, the earliest example being at Gernrode Abbey. Two reasons are suggested: that the bishop presided at one end and the abbot at the other, or that the western apse served as a baptistery. The main portal of a double-apsed church is into the side of the building, and may be richly decorated with carving.