Constructivists, such as Harvey Brown, urge that the geometries of Newtonian and special relativistic spacetimes result from the properties of matter. Whatever this may mean, it commits constructivists to the claim that these spacetime geometries can be inferred from the properties of matter without recourse to spatiotemporal presumptions or with few of them. I argue that the construction project only succeeds if constructivists antecedently presume the essential commitments of a realist conception of spacetime. These commitments can be avoided only by adopting an extreme form of operationalism.1. Introduction2. The Construction Project3. Clocks4. The Spacetime Presumed5. Lorentz Covariance Is a Property of a Matter Theory and Spacetime6. Spatial Distances and Times Elapsed Are Properties of Spacetime7. Conclusion