The closest is Saarbrücken Castle, 1 km south-west of the city centre; the most famous is Porta Nigra — #89 of 8,134 worldwide — 64 km north-west. The oldest dated site in the circle is Celtic circular wall of Otzenhausen, founded c. 350 BC.
The 100 km circle reaches into 3 countries — Germany (51), France (41), Luxembourg (39).
