The Free City of Mainz was a city-state in the Holy Roman Empire that existed from 1244 to 1462 in the late Middle Ages, which played a crucial role in the Christianization of the Germanic and Slavic communities during the Middle Ages.

The first archbishop of Mainz, Boniface, was assassinated in 754 while attempting to convert the Frisians to Christianity, and his remains are interred in Fulda.

[1] Mainz became a regular archbishopric in 781, when Boniface's successor, Lullus,[2] was granted the pallium by Pope Adrian I.

[3] Harald Klak, king of Jutland, and his followers were baptized at Mainz in 826, in the abbey of St.

[4] Rabanus Maurus, a scholar and writer, and Willigis, who initiated the construction of the current building of the Mainz Cathedral and established the Monastery of St. Stephan, were among the early archbishops of Mainz.