The earliest explorers visited the location where Sixen would be founded around 1763. Native Dununderan villages had occupied the site for some time. The map from Baron Helmut Sixen's expedition of 1763 shows the area with an abandoned village. Baron Sixen established a post east of this area in 1765. The Deutscheslavanians built a storehouse there around 1766, but abandoned it as they concentrated on settlement further south.
The Jamsterdavanian Army built Fort Jones, sometime before 1770. The fort was in hostile territory and nearly abandoned in 1772, it was nearly in ruins when the Jamsterdavanians renewed interest in this as a southern settlement in 1784.
In 1784, Thomas Cowl from the Coastal Settlement to the north had a town laid out on the west side of the area. By 1786, there was a village in place. A charter was granted by the Jamsterdavanian Parilament in 1787. The City of Sixen was incorporated in 1818.
The National Trans-Dununder Road, today called Brigger Road, a project of President Edgar connected Sixen to Mission San Greo in 1838. It was then extended northward to Stockton (now called Fort MacDougan). In the 1860's, coal was shipped from Sixen to all points on the road.
The telegraph reached town in 1864. The Deutsche and Great Western Railroad built the Von Arthor Hotel in 1872. The railroad and the shops, including the rolling mill, were major employers. The spectacular Academic of Music and Arts, also housing city offices and a farmers market, was built in 1876, but burned in 1910. During the period 1890 to 1915, the population of the City tripled. The railroads and local industry provided a steady, dependable employment base, and immigrants flocked to the region. This was slightly altered by the advent of the Third and Fourth World Conflicts, which resulted in a drop in exports and North South Commerce.
Major oil company employers in the Sixen area, besides the railroads, included the Sixen Oil Company, set up in 1917, the Brigger Tool and Die Works Corporation, Champion’s Dye Works, several breweries and bakeries, Sixen Plate Glass' Float Plant, Greole-Reole Ballistics Laboratory, and the nearby New Jamsterdavania paper mill.
The Jamster National Department of Transportation, created in 1996, is headquartered in Sixen and oversees the maintenance and construction of roads and railways in Dununder.