Concrete is the most ubiquitous construction material worldwide but also a major source of waste and CO2 emissions. Worse, it is too often crushed down prematurely for recycling or filling. Can’t we do better? We seek to reuse concrete from demolition sites by carefully sawing reinforced walls and slabs, hence generating a new circular supply chain. Reclaimed components come with their own history, their own imperfections and irregularities. Yet, they are a fully reliable construction material, amply capable of new structural feats. We designed and built the RE:CRETE footbridge, a unique post-tensioned arch that spans 10 meters, with 25 reused concrete blocks. The joints are made with regular mortar before post-tensioning. Loaded up to 1.8 tons, and deflecting less than 1.15mm, the footbridge performs just as any other one. This bridge is built out of concrete… without pouring any concrete. It opens up new pathways to drastically cut waste and CO2 emissions.