The Roman colony on the Rhine, Colonia Agrippina was the largest city in Germany in the eleventh and twelfth centuries.  Its position of commanding trade on the lower Rhine gave it great power.  In 900 less than half the area within the Roman walls were occupied.  It grew rapidly in the eleventh and twelfth centuries.  New walls were added in 1106 and 1180.  The walls of 1180 remained the boundaries of the city until the nineteenth century.