From the early 19th century to the mid-20th century, Brunswick Cross was the name given to several Prussian and German military medals with the generic name Iron Cross (German: das Eiserne Kreuz). There were several different designs yet generally shared a common pattéed shape.
They were either cast in the Duchy of Brunswick (Braunschweig) or had some relationship to that territory. Originally they were made of iron, though in later years zinc and aluminium were used.
The Duchy of Brunswick was one of oldest states in Germany, dating back to the 13th century. The territory was divided and consolidated several times and in the 18th century, the ruler of Hanover happened to be the British King George I.
George was born in Lower Saxony, inherited the Duchy of Brunswick-Lüneburg and at the age of 54 became King of Great Britain and Ireland. Thus the Brunswick Cross is found in military decorations in Britain and the Commonwealth as well as Germany.
Some of these medals have a star as a background, which is called the Brunswick Star.
For a cross found in New Brunswick, Canada, see Fredericton Cross.