The future viaduct for the extension of Metro Line 11 in Paris is a public transport service that can also become a protective public space. In this eclectic urban landscape, it must create a sense of urban unity. The primary condition for that unity is embodied in its measured, constant roof spans, which create a unifying feeling of rhythm. This rhythm must be qualified: cast steel columns make the structure coherent, providing great clarity and reflecting the special attention paid to public space. These columns are a nod to the tradition of elevated Metro lines in the 19th century. Each is 7.5 metres tall and weighs 12 tonnes.