Over 800 years since their construction, the flying buttresses of Bourges Cathedral in France still beguile engineers. The secrets behind this marvel of medieval masonry are now about to be laid bare, thanks to a group of researchers who are rebuilding it, brick by brick.

Using a laser scan of the cathedral, a team led by John Ochsendorf of the Massachusetts Institute of Technology (M.I.T) have 3D-printed thousands of bricks and are building an exact 1:50 replica. The researchers hope to use the mock-up to devise a way to gauge the stability, and thus safety, of historical buildings built of brick and stone.

Modern buildings are usually constructed around a steel framework. The steel pieces are fused, so under stress from a sinking foundation or an earthquake, say, the framework behaves as a cohesive unit.

Masonry structures are much more complex. Removing a single brick can change the pattern of stresses throughout the building. This makes it difficult to capture the forces at play, and whilst computer models and simulations help, there are a lot of inherent shortcomings.

Building the replica is painstaking work, but Ochsendorf thinks the process itself may be as valuable as the mechanics uncovered. For students of architecture and structural engineering, hands-on experience has largely given way to computer modelling. Techniques like 3D printing could be a way of reconnecting them with the craft behind the science, he says.