The Ottoman imperial arsenal on the Golden Horn, partly in diminishing use, partly evacuated and deteriorating, is one of many “frontiers” in present day Istanbul, not only because it is on the waterfront, but also because it has the potential of becoming a battlefront between different urban actors. Venice and Istanbul, the twin harbors of the past with comparable populations and similar architectural heritage, have drifted apart, one to become a well-preserved museum city coping with problems of outgoing migration and the other into a pulsating mega-city suffering from continuous incoming migration.