The Diet of Regensburg of 1623 was a meeting of the Imperial States of the Holy Roman Empire (or Fürstentag) convened by Holy Roman Emperor Ferdinand II. The meeting was not technically an imperial diet in the full sense, but a convention of princes or Deputationstag – a looser constitutional format giving the emperor greater leeway to take decisions without being bound by formal procedures. At it the Electorate of the Palatinate was transferred to Maximilian I of Bavaria. The meeting marked the high-water mark of imperial power during the Thirty Years' War. Context Frederick V, Prince-elector of the Rhine Palatinate, had been placed under the imperial ban for his role in the Bohemian Revolt of 1618–1621. His lands on the Rhine had been overrun by the army of Ferdinand's cousin Philip IV of Spain in the Palatinate campaign, and the Bohemian rebels had been defeated at the Battle of the White Mountain by an army led by another of the emperor's cousins, Duke Maximilian of Bavaria. The army of the German Catholic League, commanded by Johann Tserclaes, Count of Tilly, had defeated Frederick's allies Ernst von Mansfeld and Christian of Brunswick at the Battle of Wimpfen (6 May 1622) and Battle of Höchst (20 June 1622). It looked as though the Catholic forces had won the war, and the emperor wished to finalise Frederick's deprivation as elector with the agreement of the leading princes. On 27 July 1622 the emperor called a convention of princes to be held in Regensburg late that year. Course Emperor Ferdinand arrived in Regensburg on 24 November. He was joined within the next few days by Johann Schweikhard von Kronberg, Archbishop-Elector of Mainz, and Ferdinand of Bavaria, Archbishop-Elector of Cologne, and representatives of Lothar von Metternich, Archbishop-Elector of Trier (who did not attend in person for reasons of health). Both John George I, Elector of Saxony, and George William, Elector of Brandenburg, also sent representatives to the diet rather than take part in person, instead attending the funeral of Sophie of Brandenburg. The only major Protestant ruler to attend in person was Ludwig of Hesse-Darmstadt. The opening of the convention was delayed until 10 January, partly in the hope that more Protestant princes would decide to attend in person. The Spanish ambassador to the imperial court, Count Oñate, also attended, as did the papal nuncio, Carlo Carafa. The emperor presented the princes with several