The story behind the coin
For thirty-six years the German Empire ran on gold while one old silver coin quietly kept a privilege none of the others had. The Vereinsthaler predated the Empire itself, and when Germany went over to the Mark in 1871 it was allowed to stay in circulation at a value of three Marks. More than that, it stayed unlimited legal tender: you had to accept it in any quantity, while smaller silver coins could be refused past a fixed limit.
That was tolerable while silver was worth something close to its face value. It stopped being tolerable as silver prices sank through the late 1800s, leaving the Empire with a coin that promised far more than it contained. On 1 October 1907 the Thaler's legal-tender status ended.
The problem was habit. Germans had spent Thalers for generations, and the Mark system had nothing between the 2 Mark and the 5 Mark. So in 1908 the Empire introduced a new denomination — the 3 Mark — struck in 900-fine silver but lighter than the old Thaler it stood in for. Almost every German state issued one. People went on calling it a Thaler anyway, well into the 1930s.
Prussia's version is the one you meet most often, for the simple reason that Prussia was the Empire's giant. Berlin struck the first design continuously from 1908 to 1912 — about 22.7 million pieces. Then the Kaiser's twenty-fifth year on the throne rewrote the coin's face, and the war ended it.

