Aarau (äˈrou) [key], town (1993 pop. 15,900), capital of Aargau canton, N Switzerland, at the foot of the Jura Mts. and on the Aare River. Manufactures include bells, mathematical instruments, electrical goods, shoes, and other products. Aarau was founded c.1250; it was the temporary capital (1798) of the Helvetic Republic.