taken by Bern in April 1415. The Habsburgs had founded a number of monasteries (with some structures enduring, e.g., in Wettingen and Muri), the closing of which by the government in 1841 was a contributing factor to the outbreak of the Swiss civil war – the "Sonderbund War" – in 1847. Under the Swiss Confederation When Frederick IV of Habsburg sided with Antipope John XXIII at the Council of Constance, Emperor Sigismund placed him under the Imperial ban. In July 1414, the Pope visited Bern and received assurances from them, that they would move against the Habsburgs. A few months later the Swiss Confederation denounced the Treaty of 1412. Shortly thereafter in 1415, Bern and the rest of the Swiss Confederation used the ban as a pretext to invade the Aargau. The Confederation was able to quickly conquer the towns of Aarau, Lenzburg, Brugg and Zofingen along with most of the Habsburg castles. Bern kept the southwest portion (Zofingen, Aarburg, Aarau, Lenzburg, and Brugg), northward to the confluence of the Aare and Reuss. The important city of Baden was taken by a united Swiss army and governed by all 8 members of the Confederation. Some districts, named the Freie Ämter (free bailiwicks) – Mellingen, Muri, Villmergen, and Bremgarten, with the countship of Baden – were governed as "subject lands" by all or some of the Confederates. Shortly after the conquest of the Aargau by the Swiss, Frederick humbled himself to the Pope. The Pope reconciled with him and ordered all of the taken lands to be returned. The Swiss refused and years later after no serious attempts at re-acquisition, the Duke officially relinquished rights to the Swiss. Unteraargau or Berner Aargau Bern's portion of the Aargau came to be known as the Unteraargau, though can also be called the Berner or Bernese Aargau. In 1514 Bern expanded north into the Jura and so came into possession of several strategically important mountain passes into the Austrian Fricktal. This land was added to the Unteraargau and was directly ruled from Bern. It was divided into seven rural bailiwicks and four administrative cities, Aarau, Zofingen, Lenzburg and Brugg. While the Habsburgs were driven out, many of their minor nobles were allowed to keep their lands and offices, though over time they lost power to the Bernese government. The bailiwick administration was based on a very small staff of officials, mostly made up of