A easy to read article about the similarities between Northern & Southern Europe .

The Celto-Germanic connection unveils a captivating tale of migration, cultural encounters, and shared heritage. Through their linguistic, cultural, and genetic ties, the Celts and Germanic tribes shaped the course of European history. Exploring this connection not only deepens our understanding of ancient Europe but also highlights the rich tapestry of human civilizations and their interconnectedness.

For additional info check this other source

TLDR; both used (democratic) councils, Druids, similar culture & art, Sky Father or afraid of the Sky.