Bernardo Monanni, Secretary of the Florentine Embassy in Madrid, called this painting The Relief of the Three Cities on the Rhine by the Duke of Feria. He was undoubtedly influenced by the inscription on the lower right corner, which mentions not only Rheinfelden, but also three other neighboring cities: Waldzut, Sechim (Säckingen) and Laufenburg. The duke appears in the foreground, standing on an outcropping under a group of boulders and issuing orders to his officers. He wears the same armor and hat as in The Relief of Constance (P636) and grasps his command staff in his left hand as he points to the battlefield with his right. Further down, at the edge of the slope, a page approaches with the general’s horse. The middle ground is occupied by a platoon of armored riders from the Duke’s squadron, and the cavalry commanded by Lieutenant General Gerarldo Gambacurta. Some riders gallop down a trail alongside the cliff to succor the troops fighting in the fertile valley in front of the stronghold. In the background, the assault on the city is rendered in profuse detail, with soldiers scaling the walls and some of the troops entering through the gates and a breech in the wall. The victory is announced by a Spanish soldier on one of the cylindrical towers, who waves the Burgundian flag, with its red X on a white field. As in The Victory of Fleurus (P635), Carducho occupies the middle ground in front of the walls with a precise depiction of the order of battle of the tercios, with pikemen forming compact groups of as many as thirty rows and musketeers at their flanks. The victory of Rheinfelden, which Philip IV celebrated with a religious ceremony at the church of the Monastery of San Jerónimo el Real in Madrid, left the Spanish in full control of the line of communication between Constance and Basil. The British Museum has a preparatory drawing for this canvas whose composition barely differs from the finished work, although the officer in the foreground receiving orders from the duke wears a helmet and the walls of Rheinfelden are barely sketched in. The drawing bears the name of the besieged city, Rheinfelden, in the painter’s hand, and those of the other two -Brisach and Basil- are barely visible in the background at the upper left. Volk has pointed out that the group of two pages and a horse that appear behind the duke are drawn from Saint John of Matha Bidding his Parents Farewell (P5089), which Carducho painted around 1623 for the convent of the Trinitarios Descalzos in Madrid.

Museo Nacional del Prado, El Palacio del Rey Planeta, Museo Nacional del Prado, 2005, p.138