In The City and the Grassroots, Manuel Castells recentered the city as the site of distinctively urban social movements and reaffirmed the role of purposive social action in constructing a distinctively urban space. Although Castells’ recitation of five centuries of urban political activism documents the consistent failure of such movements to achieve their goals, his account is persistently optimistic on at least three counts. First, recentering the city reminds us that, despite the failure of transitory political movements, the city endures as an opportunity for renewed political activism. The continual possibility of change offered by the city’s ontological persistence is separate from the fate of any given political intervention. Second, regardless of its specific success or failure, each episode of urban activism establishes a new context for the next encounter, its legacy persisting in the collective memories — the stock of mnemonic capital — of which the city is the repository. Third, Castells’ emphasis on political agency affirms that, while all action is ephemeral, its constitutive re‐enactment ceaselessly provides openings for insurgency and transgression. This optimistic message is worth repeating today.