Disregarding the neutral attitude of the German electors towards the papal schism, and acting under the influence of Aeneas Sylvius Piccolomini, afterwards Pope Pius II., Frederick in 1445 made a secret treaty with Pope Eugenius IV. This developed into the Concordat of Vienna, signed in 1448 with the succeeding pope, Nicholas V., by which the king, in return for a sum of money and a promise of the imperial crown, pledged the obedience of the German people to Rome, and so checked for a time the rising tide of liberty in the German church. Taking up the quarrel between the Habsburgs and the Swiss cantons, Frederick invited the Armagnacs to attack his enemies, but after meeting with a stubborn resistance at St Jacob on the 26th of August 1444, these allies proved faithless, and the king soon lost every vestige of authority in Switzerland. In 1451 Frederick, disregarding the revolts in Austria and Hungary, travelled to Rome, where, on the 16th of March 1452, his marriage with Leonora, daughter of Edward, king of Portugal, was celebrated, and three days later he was crowned emperor by pope Nicholas. On his return he found Germany seething with indignation. His capitulation to the pope was not forgotten; his refusal to attend the diets, and his apathy in the face of Turkish aggressions, constituted a serious danger; and plans for his deposition failed only because the electors could not unite upon a rival king. In 1457 Ladislaus, king of Hungary and Bohemia, and archduke of Austria, died; Frederick failed to secure either kingdom, but obtained lower Austria, from which, however, he was soon driven by his brother Albert, who occupied Vienna. On Albert's death in 1463 the emperor united upper and lower Austria under his rule, but these possessions were constantly ravaged by George Podebrad, king of Bohemia, and by Matthias Corvinus, king of Hungary. A visit to Rome in 1468 to discuss measures against the Turks with Pope Paul II. had no result, and in 1470 Frederick began negotiations for a marriage between his son Maximilian and Mary, daughter and heiress of Charles the Bold, duke of Burgundy. The emperor met the duke at Treves in 1473, when Frederick, disliking to bestow the title of king upon Charles, left the city secretly, but brought about the marriage after the duke's death in 1477. Again attacked by Matthias, the emperor was driven from Vienna, and soon handed over the government of his lands to Maximilian, whose election as king of the Romans he vainly opposed in 1486. Frederick then retired to Linz, where he passed his time in the study of botany, alchemy and astronomy, until his death on the 19th of August 1493.