When you enter Frankfurts' Roemerberg square, the red and white church with the green copper spire can't help but catch your attention. This is Alte Nikolai, one of the oldest churches in the city. Archaeological digs done in 1988 have proven that it first existed as a small, almost square hall church built most likely around 1140 and which would have been used by the royal court living in the Staufen palace next door, though its' first official mention is in 1270. When you go inside, look for the metal inserts in the flooring that outlines where the original hall church used to be.
The steeple was once occupied by a watchman who was tasked with not only playing a tune on a horn every time a ship came and went on the Main River, but also had to watch for fires and sound the first alarms.