Megacities are filled with numerous – at first sight invisible – borders. Between rich and poor, between ethnic groups, between high and low, between dense and sprawl, in short between center and periphery. But who and what define these borders? Are they problematic? Do they tell underlying stories? Mexico City seems to be full of telling borders that generate ideas on the past, present and future of the city. There is the border of the former lake, the border of the public transport systems, the border of federal states, borders for legal abortion, and possibly many more.