Simplify the following text for a Grade 16 native English-speaking person.
Original: Some of the most important trading ports during the period include both existing and ancient cities such as Jelling ( Denmark ) , Ribe ( Denmark ) , Roskilde ( Denmark ) , Hedeby ( Denmark , now Germany ) , Aarhus ( Denmark ) , Vineta ( Pomerania ) , Truso ( Poland ) , Kaupang ( Norway ) , Birka ( Sweden ) , Bordeaux ( France ) , Jorvik ( England ) , Dublin ( Ireland ) and Aldeigjuborg ( Russia ) .
Simplified: Some of the most important trading ports during the period include both existing and ancient cities such as Aarhus ( Denmark ) , Ribe ( Denmark ) , Hedeby ( Germany ) , Vineta ( Pomerania ) , Truso ( Poland ) , Kaupang ( Norway ) , Birka ( Sweden ) , Bordeaux ( France ) , York ( England ) , Dublin ( Ireland ) and Aldeigjuborg ( Russia ) .