In 1859, Koechlin of Mulhouse built two Engerth locomotives for the PLM which were numbered 1998 and 1999. 1998 was named “La Rampe”, what gave an indication that they were intended for steep inclines. They had four driving axles and a three-axle tender whose first axle also supported the firebox. To allow the best running characteristics in curves, two running axles each were mounted in a bogie with Beugniot levers so that each group had a lateral play of 40 mm. They weighed around 50 tonnes and had a driver diameter of 1,200 mm. Their cylinders measured 540 by 560 mm.