The 15th-century power struggle that turned a German city into a battlefield
The Mainz Diocesan Feud was a brutal conflict over the archbishop's throne that pitted popes and emperors against local citizens. Between 1461 and 1463, this struggle for ecclesiastical power triggered a full-scale war, resulting in the violent sacking of Mainz and the permanent loss of its status as a free town.
The conflict began in 1459 when Diether of Isenburg was elected Archbishop of Mainz. His path to power was fraught with financial strain, as he paid 20,000 guilders in papal fees. His subsequent refusal to comply with the political and fiscal demands of Emperor Frederick III and Pope Pius II led the Pope to depose him in 1461. Adolph of Nassau was appointed as his replacement, but the city of Mainz remained loyal to Diether, sparking a war that drew in regional powers like the Palatinate, Baden, and Württemberg.
The war reached a turning point in 1462 at the Battle of Seckenheim. An alliance supporting Adolph, believing their enemy was away, invaded the Palatinate. They were caught off guard and soundly defeated by Count Palatine Frederick I, who captured key leaders, including Margrave Charles I of Baden and Bishop George of Metz. Frederick, later dubbed 'the Victorious,' extracted massive ransoms, including 45,000 guilders from the Bishop of Metz, to secure his own political standing.
The feud concluded in the city of Mainz itself. On 28 October 1462, Adolph of Nassau’s forces infiltrated the town through the Gautor gate. After twelve hours of intense street fighting that claimed 400 lives, the city was sacked. As punishment, Adolph stripped Mainz of its privileges as a free town and expelled 800 citizens. The conflict finally ended in 1463 with the Treaty of Zeilsheim, where Diether stepped down in exchange for a small principality. Remarkably, after Adolph died in 1475, Diether was re-elected archbishop and reigned until 1482.
Source: Mainz Diocesan Feud
