The Fifty Francs coin is a denomination of the Swiss Franc. Given that Switzerland has four official languages, the Franc has three different names: Franken in German, franc in French and Romansh, and franco in Italian.
In regular circulation, the denomination is served by a banknote. These gold coins are non-circulating legal tender made for collectors and struck in proof grade only. They are issued in topical series, celebrating various aspects of Swiss heritage or nature. Swissmint has issued at least one every year since 2001. Initially, both sides of the coin carried a commemorative design; starting from 2004, the obverse is the same and only the reverse changes. (It is worth mentioning that some sources consider it the other way round, and call the commemorative part the obverse; however, we are going with the standard definition, which is that "obverse" is the side which specifies the issuing authority).
The edge is inscribed with the motto DOMINUS PROVIDEBIT (The Lord will provide - a quote from the Bible, Genesis 22, 8), and thirteen stars representing the original thirteen cantons of the Swiss Federation.
This coin commemorates the 2,000th Anniversary of Aventicum in Switzerland.
Aventicum was the largest town and capital of Roman Switzerland (Helvetia or Civitas Helvetiorum). Its remains are beside the modern town of Avenches. The city was probably created in the early 1st century AD, as the capital of the recently conquered territory of the Helvetii, across the road that connected Italy to Britain, built under Claudius. Under the rule of Emperor Vespasian, who grew up there, Aventicum was raised to the status of a colonia in 72 AD, whereupon it entered its golden age. The town wall was 5.6 km long but was impracticable for defensive purposes and was doubtless intended as a display of the status of the city.
In the Christian era Aventicum was the seat of a bishopric. The most famous of its bishops was Marius Aventicensis. His terse chronicle, spanning the years 455 to 581, is one of the few sources for the 6th-century Burgundians. Shortly after the Council of Macon, in 585, Marius moved the seat from Aventicum, due to the rapid decline of the city, to Lausanne.