But a very rigorous design is not always enough to start restoration work. The real state that presents a historical building could have been modified substantially from its original state due to previous interventions, wars, seismic movements, erosion, biological aggressions or any other historical event.

So, it is necessary to join CAAD tasks with a simulation of the historical process suffered by the building. Historical data and ancient cartography must be the basis of all the CAAD works, and the quality of the computer 3D model can be established comparing it with the original available maps.

This paper explains the CAAD works and the intervention proposals for the restoration of the City Walls of Hondarribia, a small Spanish village placed in the frontier between Spain and France. These Renaissance bastioned walls were partially destroyed throughout many wars with France. The exact knowledge of their original trace and dimensions only is possible comparing the real CAD models with the plans that exist in the Spanish Military Archives since the XVIth. century.

The digital store and index of all the historical information, their comparison with real photographs of the city walls, the creation of photo realistic images with the intervention proposals, and the influence of the structural repairs in the final project will be explained in the CAAD context.