At the end of the Roman Empire in the 5th century, there were probably only about 700,000 people in the area of modern Germany. These numbers rose gradually to about 3 million by the year 1000. As elsewhere in Europe, the population of Germany then boomed for the next three centuries, possibly growing as high as 12 million people by the end of the 13th century. In addition to contributing to the growth of towns, the growing number of people increased the demand for food and arable land. One result was the push to the east, a deliberate policy of German settlement of various areas east of the Oder, Vistula, and Memel rivers. From the 12th century to the 14th century, recruiters, working for German lords, led wagon trains of Germans to settle thinly populated Slavic lands. Monastic orders such as the Cistercians and the Premonstratensians also came to the new frontier. The Teutonic Knights moved their headquarters to Marienburg in eastern Germany and led a crusade against the pagan Prussians. The knights’ defeat in 1242 by Russian prince Alexander Nevsky marked the eastern limit of German expansion, but by then most of modern-day eastern Germany, northern Poland, and the Baltic states had been overrun by German settlers.