- Aarau is a city in Switzerland, located in the canton of Aargau. It is the capital of the canton and has a population of around 21,000 people. Aarau is situated on the River Aare and is known for its beautiful old town, with well-preserved buildings from the medieval and early modern periods. The city has a rich history and was once a major center of trade and industry. Today, it is a vibrant cultural and commercial hub, with a variety of shops, restaurants, and museums. Aarau is also home to the Federal Supreme Court, which is the highest court in Switzerland.