Reichenau an der Rax is a market town in the Austrian state of Lower Austria, situated at the foot of the Rax mountain range on the Schwar…Reichenau an der Rax is a market town in the Austrian state of Lower Austria, situated at the foot of the Rax mountain range on the Schwarza river, a headstream of the Leitha. Reichenau castle was first mentioned in a 1256 deed. Duke Otto IV the Merry, who in 1327 had established the abbey of Neuberg, acquired Reichenau in 1333 and granted it to the monastery.