East German authorities began sealing the border between East and West Berlin, an action that would transform not only the political geography of Europe but also the physical structure of one of its most important cities. In the early hours of that Sunday, police, border forces and work crews tore up streets, erected barricades, installed concrete posts and stretched barbed wire across crossing points. Most sector crossings were closed and S Bahn and U Bahn connections between the two sides were interrupted. What began as a sudden barrier of wire and roadblocks was gradually expanded into the Berlin Wall, a 155 kilometre border system that surrounded West Berlin and cut through the city centre. Its impact on urban life was immediate. Streets ended abruptly, public transport routes were severed, neighborhoods were divided and buildings that had once faced ordinary city streets suddenly stood on a major political frontier. Bernauer Strasse became one of the clearest examples. The border ran directly in front of buildings on the East Berlin side, prompting some residents to escape through apartment windows into West Berlin. Within weeks, the buildings were evacuated, residents were forced to move elsewhere and windows and doors facing the border were bricked up. In later years, several buildings were demolished to create a wider and more controlled border strip. For urban and real estate history, August 13 demonstrates how political decisions can instantly alter access to land, housing, streets, transport networks and the relationship between neighborhoods. The Wall remained a defining element of Berlin until November 9, 1989, while systematic dismantling of the border installations began in 1990. August 13, 2026 marks the 65th anniversary of the start of construction, with an official commemoration being held at the Berlin Wall Memorial. The anniversary remains a powerful reminder that cities are shaped not only by architects, developers and property markets; political borders can also redraw the urban landscape and fundamentally change how people use, reach and experience property.