The archbishop of Cologne had followed a policy of territorial expansion. The great commercial interests of his city made it desirable that it should control the water-way to the sea and, if possible, a part of the coast-line. So Siegfried attempted to get possession of the lands which lay to the north and northwest, between Cologne and the sea. This brought him into conflict with the dukes of Brabant, and led to a war. In the battle of Worringen, June 6, 1228, the archbishop was defeated, taken prisoner, and held as a captive for eleven months. During his captivity his enemies took many of his possessions from him. In addition to these misfortunes the people of Cologne rebelled against him, and seized his castles, lands, and revenues. When he was finally released from captivity, he found himself in a bad plight. He was without troops, his castles were either destroyed or in the hands of his enemies, and the gates of his city were closed against him. This explains many of the things which he demanded of Adolf. Otto "with the arrow," the margrave of Brandenburg (d. 1309), received his title in a curious way. He made war on the archbishop of Magdeburg, and in a battle was struck on the head with an arrow. The point of the arrow could not be removed, but remained in his head for more than a year. On this account he was afterward called Otto "with the arrow." We, Adolf, by the grace of God count of Nassau, etc. Long before the empire was made vacant by the death of Rudolf, king of the Romans, we had vowed to God to go on a crusade, if it were possible, and to render a pleasing service to God for the remission of our sins. Now we could do much more for the honor of God and the recovery of the holy land, if we, although unworthy, were elected king of the Romans. Since our reverend father, Siegfried, archbishop of Cologne, is laboring for our election and will vote for us, of our own free will and accord we promise and bind ourselves by our word of honor and by our oath to do the following things: (1) If we are elected king of the Romans, we will protect and defend the church and all ecclesiastical persons in all their rights and liberties, and if damage is done them, we will endeavor to make it good. And we promise this especially of the church of Cologne, which has now for a long time been suffering from her heavy losses and misfortunes. (2) Even if the other electors do not vote for us, we will accept the election at the hands of the archbishop of Cologne, and we will never give up the right to the crown which his vote gives us.