After November 11, the season percolates for a few months in the more Catholic parts of Germany, culminating in a week of parades and parties before Ash Wednesday in February, when the 40-day Lent fasting season begins.
To keep the festivities under control this year, nearly 1,100 police officers and 150 public order officers have been deployed in Cologne.
The head of the department responsible for the public order office, Dirk Schmaul, urged the revellers "not to urinate in building entrances and to behave a bit."
Mayor Reker said the beauty of Cologne's Carnival is that everyone parties together: "It doesn't matter what the origin story is or the family history."
This year Cologne marks 200 years of Carnival, known as the "fifth season."
The roots of Carnival go back to the far distant past, but in the winter of 1822-23, representatives of Cologne's upper class took measures to subdue what they saw as excessively crude and anarchic Carnival behaviour.
Their model was the more cultivated Venetian Carnival. The citizens founded a "festive committee" and invented a masked procession, for which they were likely inspired by the Corpus Christi processions of the Catholic Church.
This gave rise to the large Rose Monday parades and more formalized Carnival seasons in other cities as well.
