This population explosion looked quite “American” to contemporaries; it determined Ludwigshafen's character as a “worker's city”, and created problematic shortages of housing and real estate. The solution was the expansion of the municipal area and the incorporation of the two nearest villages, Friesenheim and Mundenheim, in the years 1892 and 1899. In the area between the city centre and those two suburbs new quarters (“North” and “South”) were built after (then) modern urban development plans. Because the ground was marshy and too low to be protected from Rhine floods, all the new houses were built on raised ground, sometimes as high as 5 metres above the original ground. Visitors can see the original ground level in many backyards of Ludwigshafen, which are sometimes two floors below street level.