The King Ludwig Oak (in German: König-Ludwig-Eiche, and also Königseiche, Tausendjährige Eiche, and until the middle of the 19th century, Stolze Eiche) is an oak tree recognised as a natural monument in the Staatsbad Brückenau, a state-run spa and park two kilometres (1.2 mi) west of Bad Brückenau in the German state of Bavaria. The German Tree Archive counts the oak among the trees of national importance (National bedeutsamer Baum, NBB).Estimates of its age range between 370 and 700 years. The circumference of the trunk is about seven metres (23 ft). It is named after King Ludwig I, who frequented it during his numerous spa stays at the Staatsbad Brückenau. The oak has been described and depicted many times since 1780. Many domestic aristocrats and monarchs from abroad who were staying in Brückenau for the cure visited the oak.