When the Romans found a ford in the river (now called the Meuse) near present-day Maastricht, they could continue their way to Cologne. Since the Meuse is a rainy river, a bridge was soon built whose piers were made of stone and the canopy of wood.
The bridge was protected on both sides at the level of the ramp. These protected areas were called castellum on the west side and bridgehead Vicus on the east side. The walled area on the west side was bordered by the places, where today the Our Lady basilica, Havenstraat, Maastrichter Smedenstraat and Houtmaas are located. The Romans called this settlement "Trajectum ad Mosam" (Mosae Trajectum).
Remnants of those walls have been found in a number of places. Due to the raising of about 50 cm per century, the former ground level is now 4 to 5 meters lower than where you are walking. They were heavy walls, with semicircular towers protruding at regular intervals. At the site, now called "the Thermae," the remains of a Roman bathhouse were found during the renovation of the Stokstraat Quarter. In the pavement, the various rooms were marked with different colors. These can still be found on the spot today.
The Jeker, a tributary of the Meuse River, bordered the Castellum on the south side. The importance of the Jeker for the fortress of Maastricht is mostly underexposed. This river was dammed in later times, allowing the energy of the Jeker to be used by its inhabitants. (Grain, gunpowder, bark, paper, etc.). Later, when the city expanded its fortress, the Jeker provided the opportunity to inundate the area to the southwest.