Complex sentence: These seals show a monk in a gate; above which is an eagle highly likely stemming from the crest of the Bishop of Freising, to whom the city belonged and most likely a reference to his authority over it.
Split into simpler sentences: These seals show a monk in a gate, above which is an eagle that is very likely to stem from the crest of the Bishop of Freising. The city belonged to him and this is most likely a reference to his authority over it.