Märzen

Märzen or Märzenbier (German: March beer) is a lager that originated in Bavaria, Germany. It has a medium to full body and may vary in colour from pale through amber to dark brown. It was the beer traditionally served at the Munich Oktoberfest. The geographical indication Oktoberfestbier is protected in the EU and can only be used for Märzen that is brewed in Munich. Märzen has its origins in Bavaria, probably before the 16th century. A Bavarian brewing ordinance decreed in 1553 that beer may be brewed only between 29 September (St. Michael's Day or Michaelmas) and 23 April (St. George's Day or Georgi), as the high summertime temperatures were more likely to cause off-flavoured beer due to elevated ambient fermentation temperatures.

Source: Wikipedia