Ingolstadt is a city in the Free State of Bavaria, in the Federal Republic of Germany. It is located along the banks of the Danube, in the centre of Bavaria. As of the 2015 census, its population was 133,711. The city is the second-largest in the Bavarian administrative region with a population of 707,980 inhabitants. Ingolstadt is the birthplace of the automobile manufacturer Audi and the electronic manufacturer Siemens, as well as the motorcycle manufacturer Ducati. It is also the home of the headquarters of the German automobile club, the ADAC. The city was founded by the Roman Duke Louis the Pious in 806 as a garrison town and head of a march of the East Frankish kingdom. It was the first place in Germany to adopt Christianity in 843.