Flag of Hamburg, Germany

A big thank you to Maria, who sent this nice card of the Hamburg flag. Wikipedia has the following info:

"The civil flag shows a white castle with three towers on red background, which is used as a civil flag as a state flag for most purposes. (It was historically used as civil ensign as well.) The oldest seal with the castle is thought to date from 1241. The first flag featuring the current form was in the mid-16th century, although this was most probably a red field, a white escutcheon and red castle. After about 1623, the escutcheon began to be omitted, leaving a red castle on white or a white castle on red. It was only in 1751 that the white castle on red was decreed as the flag of Hamburg."