More than half of us now live in cities. Crowded, chaotic and bursting with life - these are places under pressure. In this brand new series, Dan Snow, Anita Rani and Ade Adepitan go behind the scenes to reveal the hidden systems and armies of people running some of the greatest cities on earth. Find out how Mexico City keeps its inhabitants safe from earthquakes, and meet local people who offer an inside look at life in metropolises like Delhi and Hong Kong. Meanwhile, Moscow's incredible architecture shows that the world's busiest cities also have some of the richest histories....