The Rose Monday Parade in Mainz is one of the largest and best known carnival parades in Germany, drawing around 500.000 spectators every year. The parade marks the peak of the carnival season, called "Fastnacht" in Mainz, which starts Nov 11th and lasts till Ash Wednesday, the beginning of the 40 days period of fasting before Holy Saturday (which are actually 46 days). So the actual date varies depending on the Easter date. 

In Mainz, Fastnacht it is a celebration of many things, including the city's history which was marked by the occupation by foreign forces, including the French and the Prussian. To this day many of the celebrants dress in uniform to celebrate the mockery of the "establishment"--whomever they may be--much as their ancestors did. Part of a multi-day celebration, the parade itself last more than 4 hours as it winds its way through the city. Rose Monday is a holiday in Mainz, so stores and offices are closed and many streets closed for traffic. 

To join the festivities as a visitor is easy: Come dressed - just about any halloween costume will do; you will see people dressed up in any costume you can imagine. But keep in mind that it is winter, so dress accordingly under your costume. Forget about parking! Leave your car outside the city and come by bus or train. Great spots to watch the parade (though very crowded) are near the Staatstheater, on the market square and at Eisgrub, a popular micro brewery in the old town.

Once you can't feel your frozen toes anymore, get into any pub and join the party and the dancing there. It is a great time and a fantastic way to experience one of Germany's traditional festivals!