Complex sentence: The square is surrounded by half a dozen of palaces, today mostly occupied by various governmental authorities, together making not only the square, but the entire island a less than vital area isolated from the rest of the city by the artery traffic route Centralbron.
Split into simpler sentences: The square is surrounded by six palaces, today mostly occupied by various governmental authorities. The area is isolated from the rest of the city by the artery traffic route Centralbron.