What was the nature of this slight tie that nominally held the Germanies together? There was the form of a central government with an emperor to execute laws and a Diet to make them. The emperor was not necessarily hereditary but was chosen by seven "electors," who were the chief princes of the realm. These seven were the archbishops of Mainz (Mayence), of Cologne, and of Trier (Trèves), the king of Bohemia, the duke of Saxony, the margrave of Brandenburg, and the count palatine of the Rhine. Not infrequently the electors used their position to extort concessions from the emperor elect which helped to destroy German unity and to promote the selfish interests of the princes. The imperial Diet was composed of the seven electors, the lesser princes (including the higher ecclesiastical dignitaries, such as bishops and abbots), and representatives of the free cities, grouped in three separate houses. The emperor was not supposed to perform any imperial act without the authorization of the Diet, and petty jealousies between its members or houses often prevented action in the Diet. The individual states, moreover, reserved to themselves the management of most affairs which in western Europe had been surrendered to the central national government. The Diet, and therefore the emperor, was without a treasury or an army, unless the individual states saw fit to act favorably upon its advice and furnish the requested quotas. The Diet resembled far more a congress of diplomats than a legislative body. [Sidenote: The Habsburgs: Weak as Emperors but Strong as Rulers of Particular States within the Holy Roman Empire] It will be readily perceived that under these circumstances the emperor as such could have little influence. Yet the fear of impending Slavic or Turkish attacks upon the eastern frontier, or other fears, frequently operated to secure the election of some prince who had sufficiently strong power of his own to stay the attack or remove the fear. In this way, Rudolph, count of Habsburg, had been chosen emperor in 1273, and in his family, with few interruptions, continued the imperial title, not only to 1500 but to the final extinction of the empire in 1806. Several of these Habsburg emperors were influential, but it must always be remembered that they owed their power not to the empire but to their own hereditary states.