The Jeker valley and the surrounding fertile land of Haspengouw were an important cultural landscape from an early age. Two very old cities lie on the Jeker, Tongeren and Maastricht, both of which claim to be the oldest city in their respective states. Tongeren was already a large city in Roman times and the capital of a civitas. Maastricht was still small at the time, but in the early Middle Ages it took over from Tongeren as an early Christian centre and trading post. The Jeker also played an important role later, within the walled cities as a source of relatively clean water (for the tannery and the cloth industry, among other things) and outside the city walls as an additional defence (as a city moat and as an inundation area; see, among other things, Jekerkanaal and De Kommen). In the 19th century, the river was very polluted and a danger to public health, which is why parts of the cities were covered over. Now that the water quality has improved, the Jeker has been reopened in Maastricht and Tongeren. The ability to flow naturally will be restored and fish will be able to swim upstream again in the future.