through Prussian territory. On 8 October 1867, service was started from Horb in Württemberg to the border town of Talhausen in Hohenzollern. On 23 July 1868, the crews of the Royal Württemberg State Railways reached Rottweil, back in Württemberg. Württemberg had signed a treaty with Baden as early as 1865, which allowed it to connect to the then-under-construction Schwarzwaldbahn (Baden), and thereby the rail net of the Grand Duchy of Baden. The state therefore constructed not only the Rottweil–Villingen line, but also a line from Rottweil via Spaichingen to Tuttlingen, which opened on 15 July 1869. From Tuttlingen, the Royal Württemberg State Railways extended construction to the border town of Immendingen in Baden, which was done on 26 July 1870, and which meant that the connection to the Black Forest Railway (Baden) had been successfully completed. Starting in 1870, it was then possible to leave the capital in Stuttgart, and to travel by rail via Plochingen, Reutlingen, Horb, Rottweil, and Tuttlingen to Immendingen on Württemberg-owned tracks, and then to connect on to Singen, the Baden-Swiss border near Schaffhausen, and the western edge of Lake Constance (Bodensee). Two trains made the daily trip between Stuttgart and Tuttlingen, and an additional train traveled between Stuttgart and Rottweil only. Connections to Immendingen were initially only possible via Rottweil or Tuttlingen. The primary locomotive on this trip at the time was the Württemberg F class of steam locomotive, which took between 7 and 8 hours to cover the distance. Construction of the Eutingen–Horb and Horb–Stuttgart sections (1874–1879) The big disadvantage of this traffic routing was the fact that the tracks would follow the Neckar valley in a lengthy loop, which would make travel times quite a bit longer. However, the Royal Württemberg State Railways did not pursue a more direct connection between Horb and Stuttgart, primarily due to engineering issues to do with the grade between the two points. The partial section between Eutingen and the connection point to the Obere Neckarbahn in Horb was already completed by 1 June 1874. The aim of this construction was not the connection between Horb, via the Gäu and Böblingen, to Stuttgart, but was done to complete the Nagold Valley Railway from Pforzheim to Horb. This line had been started in 1868, and its connection to Horb meant the establishment of Horb as an important railway node. In 1874, the parts of the full Gäubahn Stuttgart–Singen consisted