Complex sentence: It is curious that the lion as a heraldic symbol was mostly used in border territories and neighbouring countries of the Holy Roman Empire; it was a way of showing independence from the emperor, who used an eagle in his personal arms.
Split into simpler sentences: It is curious that the lion as a heraldic symbol was mostly used in border territories and neighbouring countries of the Holy Roman Empire. It was in all likelihood a way of showing independence from the emperor, who used an eagle in his personal arms.