The northern rump of Middle Francia, inherited by Lothair II in the 855 partition of his father Lothair I's realm: a corridor from Frisia and the Low Countries south through the Rhineland, anchored on Aachen, repeatedly fought over by West and East Francia after Lothair II died heirless.
Partitioned between East and West Francia after 869-870 (Treaty of Meerssen); reunited briefly, then absorbed into East Francia (the future Holy Roman Empire) by 959 as the stem duchy of Lotharingia/Lorraine.
The atlas holds 2 border frames for Lotharingia — the shape you scrub through changes in 855 · 898.
Dedicated popular history specifically of the Lotharingia/Lorraine-Low Countries corridor, tracing it from its Carolingian founding.