Marca Geronis

The Marca Geronis or March of Gero is a historiographical term, derived from titles and offices of early medieval military commanders and governors of various German frontier jurisdictions in lands of Polabian Slavs. In primary sources, such as the Thietmar's Chronicle, the term was used in relation to count Gero II (d. 1015), whose frontier province (march) was mentioned as the count Gero’s march (Latin: Geronis marcham comitis; German: Mark des Grafen Gero). In later historiography, the same term was borrowed and reapplied as a descriptive designation for an earlier frontier jurisdiction of count Gero I (d. 965), a prominent noble from the Duchy of Saxony, who was appointed margrave (Latin: marchio) by king and emperor Otto I (936-973). The nature and scope of his jurisdiction as a margrave is indicated in several sources, such as the 11th century Thietmar's Chronicle, that mentions Gero I as Margrave of the East (Latin: Gero Orientalium marchio; German: Markgraf Gero von der Ostmark).

Various sources contain data on frequent and continuous involvement of margrave Gero I in German expansion towards the east, into the lands of Polabian Slavs, and thus in traditional (early modern) historiography he was regarded not only as frontier commander, but also as an effective provincial governor in the subdued Slavic regions, thus applying the term March of Gero for his province too. Newer scholarly analyses have shown that copies of some charters that contain data on early German marches in Slavic regions should be considered as interpolated or even forged, thus leading modern researches to question or reject various traditional views regarding the scope and effective existence of some frontier jurisdictions, as described in older historiography.

Among complexities involved in ascertaining the territoriality of the march over which Gero I ruled is the nature of the margravial title and office in tenth-century Saxony, and Germany in general, since it may have signified territorial governance, or a military command over a frontier region, with additional duties regarding the collecting of tributes from dependent peoples and tribes, as attested by activities of Gero I, but on the other hand may have been just an honorific title for especially powerful counts.