Crossing the Italian-Austrian border, the Brenner Pass separates the Ötztal Alps and Zillertal Alps and has been in use as a trading route since the 14th century. The lowest of the Alpine passes at 985 m (3,232 ft), the Semmering crosses from Lower Austria to Styria; since the 12th century when a hospice was built there it has seen continuous use. A railroad with a tunnel 1 mile (1.6 km) long was built along the route of the pass in the mid-19th century. With a summit of 2,469 m (8,100 ft), the Great St. Bernard Pass is one of the highest in the Alps, crossing the Italian-Swiss border east of the Pennine Alps along the flanks of Mont Blanc. The pass was used by Napoleon Bonaparte to cross 40,000 troops in 1800. The Saint Gotthard Pass crosses from Central Switzerland to Ticino; in the late 19th century the 14 km (9 mi) long Saint Gotthard Tunnel was built connecting Lucerne in Switzerland, with Milan in Italy. The Mont Cenis pass has been a major commercial road between Western Europe and Italy. Now the pass has been supplanted by the Fréjus Road and Rail tunnel. At 2,756 m (9,042 ft), the Stelvio Pass in northern Italy is one of the highest of the Alpine passes; the road was built in the 1820s. The highest pass in the alps is the col de l'Iseran in Savoy (France) at 2,770 m (9,088 ft).

What seperates the Otztal Alps and Zillertal Alps?