Was George Orwell an Optimist?
Thelonious Monk - Monk's Dream // Benny Carter - The King // Charles McPherson - Manhattan Nocturne // Art Pepper - Smack Up // Dudu Pukwana - In The Townships
In the side section they indeed mention upgrading from level zero is only allowed in free spaces; but I assumed that free here means not already having a pyramid.
If controlled by an opponent is also not 'free' what about having a troop of your own? Also this speaks explicitly about new pyramids, not about improving an existing one. Is this then disallowed in occupied districts by implication?
Bottom line, I don't agree it is in the rules, although I'll take your answer as the correct resolution.
Thx for answering
I think you're right to question my first answer; I don't like it much either. But I just looked again and found something better: the rule for Pyramids (first paragraph on page 2, final sentence):
Each pyramid must be placed in a different district in the players' city.
(I added the bold for emphasis, but the misplaced apostrophe is exactly how it appears in my copy of the rules.)