Kreuznach passed to the Kingdom of Prussia in 1815 and from 1816 it belonged to the Regierungsbezirk of Koblenz in the province of the Grand Duchy of the Lower Rhine (as of 1822 the Rhine Province) and was a border town with two neighbouring states, the Grand Duchy of Hesse to the east and the Bavarian exclave of the Palatinate to the south. The two saltworks, which had now apparently been taken away from Napoleon's sister, were from 1816 to 1897 Grand-Ducal-Hessian state property on Prussian territory. In 1817, Johann Erhard Prieger opened the first bathing parlour with briny water and thereby laid the groundwork for the fast-growing spa business. In 1843, Karl Marx married Jenny von Westphalen in Kreuznach, presumably at the Wilhelmskirche (William's Church), which had been built between 1698 and 1700 and was later, in 1968, all but torn down, leaving only the churchtower. In Kreuznach, Marx set down considerable portions of his manuscript Critique of Hegel's Philosophy of Right (Zur Kritik der Hegelschen Rechtsphilosophie) in 1843. Clara Schumann, who was attending the spa in Kreuznach, and her half-sister Marie Wieck gave a concert at the spa house in 1860. With the building of the Nahe Valley Railway from Bingerbrück to Saarbrücken in 1858/1860, the groundwork was laid for the town's industrialisation. This, along with the ever-growing income from the spa, led after years of stagnation to an economic boost for the town's development. Nevertheless, the railway was not built for industry and spa-goers alone, but also as a logistical supply line for a war that was expected to break out with France. Before this, though, right at Kreuznach's town limits, Prussia and Bavaria once again stood at odds with each other in 1866. Thinking that was not influenced by this led to another railway line being built even before the First World War, the "strategic railway" from Bad Münster by way of Staudernheim, Meisenheim, Lauterecken and Kusel towards the west, making Kreuznach into an important contributor to transport towards the west. Only about 1950 were parts of this line torn up and abandoned. Today, between Staudernheim and Kusel, it serves as a tourist attraction for those who wish to ride draisines. In 1891, three members of the Franciscan Brothers of the Holy Cross came to live in Kreuznach. In 1893, they took over the hospital Kiskys-Wörth, which as of 1905 bore the name St. Marienwörth. Since