were no vicars appointed to the dioceses of Gaul and Dacia, because the praetorian prefects of Gaul and Illyricum were resident. When the prefect of Italy was in Milan, a vicar for Illyricum was appointed to reside in Sirmium; when the prefect resided in Sirmium, the post was lapsed, and a vicar was appointed to reside in Milan in place of the prefect. In the course of the 5th century, the Western Empire was overrun by the invasions of Germanic tribes. However, the prefecture of Italy was retained by the new Ostrogothic Kingdom, which was still de jure part of the Empire, and Ostrogothic king Theodoric the Great even re-established the prefecture of Gaul in the small portion of Gaul he conquered in the 510s. After the reconquest of Northern Africa by the Eastern Empire during the Vandalic War of 533–534, the new provinces were grouped by emperor Justinian I into a new praetorian prefecture of Africa, which would later be transformed into the Exarchate of Africa. The praetorian prefecture of Italy was also re-established after the end of the Gothic War, before it too evolved into an exarchate. In the East, the prefectures would continue to function until the mid-7th century, when the loss of most eastern provinces to the Muslim conquest and of the Balkans to Slavic tribes led to the creation of the Theme system. In the meantime, however, reforms under Heraclius had stripped the prefect from a number of his subordinate financial bureaux, which were set up as independent departments under logothetes. The last time the prefect of the East is directly attested comes from a law of 629. According to some scholars, however, traces of the system survived into the early 9th century: Ernst Stein demonstrated that some aspects of the Illyrian prefecture survived in the administration of Thessalonica, while John Haldon, based on sigillographic evidence and references in the Byzantine Taktika, has documented the survival of the earlier civilian provincial administration within the theme system, with the prefect in Constantinople possibly in a supervisory capability, until the 840s. Authority and powers of the prefect Originally, the praetorian prefects were drawn from the equestrian class. Constantine's reforms entailed the reservation of this office for members of the senatorial class, and its prestige and authority were raised to the highest level, so that contemporary writers refer to it as the "supreme office". In the divided Empire,