In August 1620, Don Ambrosio Spinola, as commander-in-chief of the Army of Flanders, invaded the Palatinate from the Spanish Netherlands and advanced over Frankfurt.

[6] The attention of the Marquis focused on Oppenheim, a town of strategic importance because their bridge guarded the entrance to the heart of the Electorate of the Palatinate.

Joachim Ernst, Margrave of Brandenburg-Ansbach, who commanded the Protestant army stationed in Oppenheim and surroundings, about 24,000 soldiers, took the bait and went with most of his troops to Worms, leaving a small garrison in Oppehneim.

[5] Spinola, between therefore, taking advantage of the night approached to Oppenheim, where he arrived with his army at dawn on 14 September, with the assault on the positions of the town not long in coming.

[8] The various garrisons that had been left in the conquered places had driven down the number of the Spanish army, so that Spinola decided to quarter in Oppenheim, and requested reinforcements from Archduke Albert in Brussels.