What is "martinstor"

The Martinstor (English Martin's Gate), a former town fortification on Kaiser-Joseph-Straße, is the older of the two gates of Freiburg im Breisgau that have been preserved since medieval times. Both gates, the Martinstor and the Schwabentor, are located in the city centre. In medieval times the Martinstor was also known as Norsinger Tor.