Braunschweiger Mumme was a high-alcohol beer that was thick and sweet. It's believed that it was first brewed as far back as the 14th century in Brunswick, Germany, and later imported to Great Britain, probably after the Hanover electors became kings of England. In Britain it was simply called mum or mumm.
During the 16th and 17th centuries mumme was very popular throughout Europe because its high alcohol content allowed it to survive long periods of hot weather without spoiling.
It came in two variations: Stadt-Mumme, meant to be drunk immediately; and the more heavily hopped Schiff-Mumme, intended for export of for use on long sea voyages. The beer's thick consistency came from a long boil, first of the whole mash for one and a quarter hours then of the wort and hops for another three hours. Mumme usually was made with barley, wheat and oats, and hopped. A surviving English recipe for mumme from 1680 includes herbs, berries, birch and fir tips, beans, and unbroken eggs.
Oddly, sometime in the 18th century mumme changed completely in character, becoming a non-alcoholic malt tonic, something to be taken for headaches and other ailments. It survives in this form today. It's usually drunk mixed with ordinary pils.