Arnoldstein (Podklošter, Oristagno) is a market town in the district of Villach-Land in the Austrian state of Carinthia.
Arnoldstein is located at Austria's southern border between the Carnic Alps and the Karawanken mountain range, near the confluence of the Gailitz (Slovene: Ziljica, Italian: Slizza) and the Gail River (Slovene: Zilja, Italian: Zeglia). The tripoint with Tarvisio in Italy and Kranjska Gora in Slovenia is south of the town at the top of the Ofen (Slovene: Peč, Italian: Monte Forno) at 1,509m/4,951 ft. Today there is a marker at this location.
Arnoldstein can be reached via the A2 Süd Autobahn from Vienna and the parallel Austrian Southern Railway (Rudolfsbahn), running from Klagenfurt to the Italian border, where it is continued by the Italian Pontebbana line to Udine.
Arnoldstein is divided into six Katastralgemeinden: Arnoldstein (Podklošter), Hart (Ločilo), Maglern (Megvarje), Pöckau (Peče), Riegersdorf (Rikarja vas), and Seltschach (Sovče). It can be further divided into 21 Ortschaften (with population totals 2001):
The area around Arnoldstein was already settled in ancient times, when a Roman Road along the Gailitz creek connected Aquileia with Virunum near present-day Klagenfurt, capital of the Noricum province.
Arnoldstein's name derives from the alleged founder of its castle, one knight Arnold, probably a ministerialis serving the Bishops of Bamberg. Upon his coronation in 1014, Emperor Henry II had granted large estates in the Duchy of Carinthia to the Bamberg diocese, that originally had been a possession of the Patriarchs of Aquileia. The castle itself was first mentioned about 1085, here Bishop Otto of Bamberg established a Benedictine abbey in 1106 to secure his Carinthian fiefs. Nevertheless, in 1176, the monks had to accept the secular Vogt overlordship of the Carinthian Sponheim dukes. In the mid-14th century their estates were devastated both by the 1348 Friuli earthquake and the Black Death pandemic.