Complex sentence: Rutupiae was the Roman name for Richborough in Kent and was the site of a major triumphial arch, now destroyed; although the ruins of the Roman fort (Richborough Castle) still stand.
Split into simpler sentences: Rutupiae was the Roman name for Richborough in Kent and was the site of a major triumphial arch, now destroyed. The ruins of the Roman fort (Richborough Castle) still stand.