The quaestura exercitus was a peculiar administrative district of the Eastern Roman Empire with a seat in Odessus (present-day Varna) established by Emperor Justinian I (r. 527–565) on May 18, 536.
Territorially, the quaestura exercitus contained the Roman provinces of Moesia Inferior and Scythia Minor, located in the lower Danube region, as well as the provinces of Cyprus, Caria, and the Aegean Islands (i.e. the Cyclades). All of these provinces were detached from the Praetorian prefecture of the East and placed under the authority of a new army official known as the quaestor exercitus ("Quaestor of the army"). The authority of the quaestor was the equivalent to that of a magister militum. Since the strategically vital Danubian provinces were economically impoverished, the purpose of the quaestura exercitus was to help support the troops that were stationed there. By connecting the lower Danubian provinces with wealthier provinces, Justinian was able to transport supplies via the Black Sea. This territorial restructuring relieved both the destitute populations and devastated countryside of the Danubian provinces from sustaining any stationed troops. There is a lack of subsequent evidence on the history of the quaestura exercitus. However, since the position of quaestor was still existent during the mid-570s, this indicates that the overall territorial unit achieved a modicum of success.
Ultimately, the Danubian provinces associated with the quaestura exercitus did not survive the Slav and Avar invasions of the Balkans in the 7th century. However, isolated fortresses on the Danube delta and along the coast of the Black Sea were maintained via supplies by sea, and there is evidence that the great naval corps of the Karabisianoi was first formed by the remainders of the quaestura. Lead seals from Moesia Inferior and Scythia Minor provide evidence supporting the existence of the quaestura exercitus. Specifically, thirteen imperial seals (nine of which are from Justinian) demonstrate that communications between officials from Scythia Minor and Constantinople occurred on a somewhat regular basis.
- Velkov 1977, p. 62: "In 536 (May 18) a peculiar administrative district was created - quaestura exercitus. It included Lower Moesia and Scythia (separated from the diocese of Thrace), the Cyclades, Caria, and Cyprus."
- Maas 2005, p. 120: "This infrastructure possessed flexibility and scope for adaptation according to circumstances specific to different parts of the empire, as demonstrated by Justinian's establishment of the quaestura exercitus (quaestorship of the army) in 536, whereby the provinces of Moesia and Scythia on the lower Danube and the Asian provinces of Caria, Cyprus, and the Islands were detached from the praetorian prefecture of the east and placed under the authority of a new official, the quaestor of the army."
- Haldon 1999, p. 68: "An important new field command, the quaestura exercitus, had been introduced during the reign of Justinian. It was equivalent to that of a magister militum, placed under the authority of an officer entitled quaestor, with authority over troops based in the Danube frontier zone (the provinces of Scythia and Moesia II), but including also the Asia Minor coastal province of Caria and the Aegean islands."
- Maas 2005, p. 120: "The Danubian provinces, strategically critical but economically poor, had long struggled to support the troops stationed in them, a problem Justinian sought to solve by linking them in this way with the wealthier and more secure Asian provinces that could transport supplies via the Black Sea to the lower Danube. Although evidence about the subsequent history of this arrangement is limited, the post of quaestor was still in existence in the mid 570s, suggesting that it achieved some success."
- Haldon 1999, p. 68: "The purpose appears to have been to supply the Danube frontier forces by sea from a secure hinterland, thus sparing the hard-pressed population and ravaged countryside of the frontier districts where the armies were based."
- Haldon 1999, p. 74: "The districts ascribed to the old quaestura exercitus established by Justinian did not survive the Slav and Avar invasions of the Balkan provinces (although isolated fortresses on the Danube delta and along the coast of the Black Sea were maintained and supplied by sea); but its Aegean regions remained, as before, the source of men, ships and resources for a maritime corps known in the later seventh century as the "ship troops", or Karabisianoi, probably based at first on Rhodes, although also drawing its soldiers from the mainland."
- Curta 2001, pp. 185–186: "Ever since A. H. Jones interpreted the quaestura exercitus as an administrative reform designed to ensure a continuous food supply for troops stationed on the Thracian border, scholars insisted that the attributions of the quaestor were primarily financial. He was directly responsible for the annona (provisioning) of the army in Moesia Inferior and Scythia Minor. In addition, lead seals found in the region point to communication of some regularity between the two Balkan provinces included in the quaestura exercitus and the central government. Thirteen imperial seals, nine of which are from Justinian, demonstrate that officials in Scythia Minor received letters and written orders from the emperor."
- Curta, Florin (2001). The Making of the Slavs: History and Archaeology of the Lower Danube Region, c. 500–700. Cambridge: Cambridge University Press.
- Maas, Michael (2005). The Cambridge Companion to the Age of Justinian. Cambridge, United Kingdom: Cambridge University Press. ISBN 0-521-81746-3.
- Haldon, John F. (1999). Warfare, State and Society in the Byzantine World, 565-1204. London, United Kingdom: Routledge. ISBN 1-85728-494-1.
- Velkov, Velizar Iv. (1977). Cities in Thrace and Dacia in Late Antiquity: (Studies and Materials). Amsterdam, The Netherlands: A. M. Hakkert.