First Fortification of Salzburg:
There was a castle on the Nonnberg since Roman times; even older fortifications were found on the Rainberg, they are of Celtic origin. In the 11th century, the development of the current Festung Hohensalzburg started in the course of the Investiturstreit, a struggle for power between Pope and German Emperor. In 1291, there was also a ring of walls around the bishop′s palace near today′s cathedral. This wall had three gates and was incorporated into the so-called "first fortification".
This first fortification of Salzburg ("Erste Stadtbefestigung") is based on an order by Emperor Friedrich II to all the princes of the empire to fortify their capitals. Subsequently, a ring of walls was built around Salzburg in the first half of the 13th century. The city seal of 1249 already depicts two gates, a tower and walls - the base for the city coat of arms. Note for the following descriptions that "Tor" means "Gate" (in this context, with a tower and defence facilities around it).
On the left side of the river Salzach, the fortifications included the Inneres Nonntaltor (roughly where today′s Landesgericht has its rear entrance); the Kumpfmühltor (behind today′s humanities faculty building near Papagenoplatz; a wall from the Pfeifergasse to the Waagplatz, along Judengasse, then the Klampferertor about 50 metres upstream the current Staatsbrücke bridge, there was the Rathaustor, then the Tränketor, finally the Bürgerspitaltor at the onset of the Getreidegasse (also called Inneres Klausentor or Inneres Gstättentor, not to be confused with the current Gstättentor at Bürgerspital). On the right side of the Altstadt, there was the Inneres Lederertor and the Ostertor (even though the latter might have been built only in 1280).
Further gates and walls were built between 1250 and 1450, especially on the badly fortified right side of the Salzach: Klausentor (1250); the Kotbrücktor near the Bruderhof (1350); Bergstraßtor at Dreifaltigkeitsgasse (1350); Galgentor or Linzertor at Linzergasse (1373, a very important one); Inneres Steintor (at some point in the early 15th century) at Steingasse; Löchl-Bogen near Griesgasse (late 14th century); Wartlsteintor in Mülln (late 14th century); Laufenertor (late 14th or early 15th century).
City Walls on the SalzburgWiki (German)