Praesental army

Every immediate imperial prince is entitled to raise an army of his own. The emperor is by tradition elected from the ranks of princes, and that means he is also entitled to raise a host. This host, called the Praesental army - the army in the imperial presence - is special, as it does not change with the change of the emperor, as one would normally expect. 
The Praesental army is traditionally recruited from the picked regiments - often Household and Life guard of the princes - and held in constant service as a standing army, in contrast to the usual system of allotment that does not lend itself to having the army on standby. 
The Praesental army is meant to give the emperor the means of accomplishing certain military goals without the need to call for a general levy and rely on contingents from the princely armies, and is paid for from the imperial treasury directly. Curiously, they do not swear an oath of allegiance to the emperor upon his coronation, but rather to the imperial rank and distinction upon their induction in the prestigious host. This is meant to deter treason better, but mostly serves as a convenient way of avoiding binding the Praesental army to any one house that occupies the throne.
The standing nature of the Praesental army lends itself to frequent drills, and this makes them a rather formidable fighting force, forming the core of the Imperial guard on campaign - along with the Household and Life guard and detachments from princely guard regiments. In peacetime they are tasked with manning the crucial imperial fortresses, primarily in the Thirteen Cities region, and castle Hengstenberg, and are generally billeted or encamped in the Thirteen Cities as well, except for routinely rotated detachments.
The Praesental army follows the general imperial military tradition of bestowing honourary colonelships onto the princes, thus both making them contribute to their regiments' maintenance and allowing them a share of their glory. Praesental regiments, however, do not grant their honourary colonels the usual degree of freedom in the appointment of the officers above junior ranks, as this always requires the consent of either the emperor (which is rarely used) or the commander of the Praesental army - the Count of the God-saved Imperial Retinue, custodian of the Thirteen Cities and the imperial heartland, appointed by and answering to the emperor himself. This does not detract from the value of such colonelships, for the glory and share of loot to be had are generally great, and this great honour is usually only bestowed on proven servants and able generals. 
Service in the Praesental army in the capacity of a private with the subsequent promotions all the way to the acting officer ranks, including acting colonels, is also a popular route for the younger noble sons that cannot inherit their father's propery, but can inherit noble distinctions - an alternative to the imperial civil service. Such unlanded nobles gain a good chance at getting noticed and richly rewarded, for example, with a position in the Household or Life guard or a landed title, by serving in the distinguished Praesental ranks.
The Praesental army has an almost unbroken history of more than a thousand years, only interrupted by a seventy-year period of abolition during Theodahad's reign, brought about by severe depletion of both the quality troops and imperial finances. It was eventually reestablished by Adalbert II and continues to exist ever since, notably preserving its fighting distinction.