Basilika St. Kastor

Basilika St. Kastor is Koblenz's oldest church, consecrated in 836 under Emperor Louis the Pious at the confluence of the Rhine and Moselle rivers, and it holds particular significance in European history as the site associated with negotiations leading to the 843 Treaty of Verdun, which divided the Carolingian Empire among Louis the Pious's three grandsons into territories that roughly prefigured the later kingdoms of West Francia, Middle Francia, and East Francia. The surviving church combines its Carolingian-era foundations with substantial Romanesque rebuilding completed in the 12th century, including the twin west towers and the basilica's characteristic rounded arches, and later Gothic vaulting added to the nave in the 15th century, giving the building a layered architectural history typical of Rhineland churches with early medieval origins. The church survived the wartime destruction that damaged much of central Koblenz in 1944, and post-war restoration preserved its Romanesque and Gothic fabric largely intact. A notable feature in the adjoining Kastorbrunnen fountain outside the church commemorates Napoleon's Russian campaign, with an inscription later mockingly amended by Prussian forces after his defeat, an example of the site's continued entanglement with major European political events across a millennium. Inside, the basilica preserves Romanesque capitals, a Gothic choir, and later Baroque furnishings, presented as a living parish church rather than a museum, with visitors free to explore the nave and side chapels at their own pace and information panels explaining the church's Carolingian origins and Treaty of Verdun connection.