The Bible says that God once wrote on the wall in Babylon when it came to the rather negative evaluation of Nebuchadnezzar. From Nebuchadnezzar, in turn, it is assumed that in its time building inscriptions were put on Ishtar gate for its glory. 
It will always be an exciting question as to who writes, draws or paints on walls when and why. This is true across many cultures, and likewise an interrelationship could be traced through history: on the one hand, the commissioned design of official interpretation reading, and on the other, the self-authorized use of the wall. Or to put it differently: on the one hand the tendency to create a political or aesthetic consensus (or at least to claim this) and on the other hand the objection against exactly this request, which then is motivated by the desire to also exist in this world or simply to want to express one’s own opinion here.

Walls are by no means neutral places. They separate between public and private, their surfaces usually form barriers to a clear view, their material serves load-bearing, isolating, protective, or exclusionary functionality. So it’s rather obvious to perceive them as a means of constraint, especially when you see yourself on the wrong side. Such views tend to occur particularly often whenever power issues are brought up publicly and social or aesthetic consent becomes a subject of discussion. Historically, this can be traced for the French as well as the Russian revolutions, for the student unrest of the 1960s, the German Autumn in the mid-1970s, the revolution in Iran in 1979, the literarily noted year of 1984, or for the fall of the Berlin Wall in 1989. In addition, there is almost always the discussion of real estate speculation and squatting (which, with quite deliberate references to war events, they called „Häuserkampf” [house-to-house fighting]).

Cologne’s political microclimate – with all the often and gladly claimed Cologne peculiarity – reflects such world-political events on the walls. Anyone who strolled through the Cathedral City in the 1980s saw exactly what was going on in world politics: NATO re-armament during the Cold War, disputes on the future of the former Stollwerck factory, the beacon of Chernobyl. Even the advertising industry’s campaign of conquest in public space, which can often only be perceived by comparing photos in the medium term, was already a topic on the walls in selected cases.