The Episcopal Frontier
The main link below leads to a StoryMap (a series of maps presented with unified commentary) intended to illustrate the evolution of institutions along the northern and northeastern frontiers of Christendom. In particular, it traces chronologically the establishment of bishoprics in Germany and beyond, from the mid-seventh century to the beginning of the 13th.1
The maps may also be accessed individually:
Map I: 650 C.E.
Maps IIA + IIB: 747 C.E. + 756 C.E.
Map III: 820 C.E.
Maps IVA + IVB: 875 C.E. + 910 C.E.
Maps VA + VB: 975 C.E. + 990 C.E.
Map VI: 1010 C.E.
Map VII: 1050 C.E.a
Map VIII: 1075 C.E.
Map IX: 1125 C.E.
Map X: 1155 C.E.
Map XI: 1175 C.E.
Maps XIIA + XIIB: 1190 C.E. + 1205 C.E.