Simplify the following text for a Grade 8 native English-speaking person.
Original: Saint-Denis is a sub-prefecture of the Seine-Saint-Denis dÃ partement , and is the seat of the Arrondissement of Saint-Denis .
Simplified: Saint-Denis is a sous-pr Ã fecture of the Seine-Saint-Denis dÃ partement , being the seat of the Arrondissement of Saint-Denis .