Having somewhat accustomed the people to this new form of military service, and constantly exercised the nobles and their men-at-arms in sham fights and tournaments (which he is said to have first instituted), Henry now tested them in actual war. The Slavonic tribes east of the Elbe had become the natural and hereditary enemies of the Germans, and an attack upon them hardly required a pretext. The present province of Brandenburg, the basis of the Prussian kingdom, was conquered by Henry in 928; and then, after a successful invasion of Bohemia, he gradually extended his annexation to the Oder. The most of the Slavonic population were slaughtered without mercy, and the Saxons and Thuringians, spreading eastward, took possession of their vacant lands. Finally, in 932, Henry conquered Lusatia (now Eastern Saxony); Bohemia was already tributary, and his whole eastern frontier was thereby advanced from the Baltic at Stettin to the Danube at Vienna. [Sidenote: 933. VICTORY OVER THE HUNGARIANS.] By this time the nine years of truce with the Hungarians were at an end, and when the ambassadors of the latter came to the German Court to receive their tribute, they were sent back with empty hands. A tradition states that Henry ordered an old, mangy dog to be given to them, instead of the usual gold and silver. A declaration of war followed, as he had anticipated; but the Hungarians seem to have surprised him by the rapidity of their movements. Contrary to their previous custom, they undertook a winter campaign, overrunning Thuringia and Saxony in such immense numbers that the king did not immediately venture to oppose them. He waited until their forces were divided in the search for plunder, then fell upon a part and defeated them. Shortly afterwards he moved against their main army, and on the 15th of March, 933, after a bloody battle (which is believed to have been fought in the vicinity of Merseburg), was again conqueror. The Hungarians fled, leaving their camp, treasures and accumulated plunder in Henry's hands. They were never again dangerous to Northern Germany.