Map link: https://pt.m.wikipedia.org/wiki/L%C3%ADngua_protogerm%C3%A2nica#/media/Ficheiro%3ANordic_Bronze_Age.png
Although the map is painted the part where the protagonist did not conquer this entire area, but the protagonist's son conquered the Jutland peninsula, and his grandson the coastal areas of Scandinavia.
This is purposefully unclear in the first chapter but the capital is Hamburg/Vienna the protagonist's tribe lives on a tributary of the Elbe River but because of the protagonist they came closer to where Hamburg was founded and founded the city of Vienna there.