Bern's strong bent for territorial extension was quite a match for the encroaching tendencies of the Habsburgs. To get a footing in the canton the latter made use of a crime committed amongst the Kyburger. That illustrious house, well-nigh ruined morally and financially, had been compelled by its adverse fortunes to place in the Church a younger son, Eberhard. The young man submitted with great reluctance. Happening to fall to a quarrel with Hartmann, at the castle of Thun, high words arose and were succeeded by blows, and Hartmann was slain. This was in 1332. On the plea of avenging the murder, the Habsburgs set up a claim to the Kyburg property. Bern however confirmed the count in his possessions, and purchasing Thun from him, returned it as a fief, requiring him to give an undertaking that Burgdorf should never be mortgaged without her knowledge and consent. But Eberhard gradually forgot the services Bern had rendered his house, and, fearing her power, veered round to Freiburg, and became a citizen of that town. The differences then swelled into an outbreak, which had been for some time impending. Bern, it is to be noted, had in many ways got the start of the sister city; for instance, she had become an imperial free city in the year 1218, on the extinction of the Zaeringer, and this had given her a considerable lift. Then, in 1324, Bern had secured the mortgage of Laupen, an excellent stronghold on the Saane, and had driven the Freiburger from the district. And in 1331, after the house of Kyburg had joined its fortunes with those of Freiburg, the strong fortress of Gümminen had been demolished, as well as many Kyburg castles. Gümminen belonged to her rival, and was a place of singular strategical importance.