anastylosis (from the Greek ἀνά "upward" and στύλος "column") is an archaeological term that designates the technique of reconstructing a monument in ruins from its dispersed elements, which are relocated to their original position thanks to the methodical study of the fit between the parts.[1]​.

Anastylosis can be a simple operation in the case of large-rigged ancient monuments "Rig (construction)"), where each block had a defined place; However, it is much more difficult to do in monuments with interchangeable stones such as medieval buildings. Partial anastylosis of these is only possible for parts found in connection (generally in excavations).

When elements are missing, modern element additions can be used (cement, plaster, resin, etc.), in which case it is important that the new materials are easily distinguishable, to avoid erroneous interpretation of the result.[2]​.

Prudence is necessary to solve anastylosis, and in all cases the choice of this technique must be preceded by a collegiate scientific study. This raises a number of questions:

The International Charter of Venice of 1964, which establishes the common principles that should govern the conservation and restoration of heritage, details the criteria for anastylosis.[3]​.

First, the original condition of the structure must be scientifically confirmed.

Second, the proper location of each recovered component must be determined.

Third, complementary components must be limited to those necessary for stability (i.e., substitute components can never be on top) and must be recognizable as replacement materials.

Fourth, new construction in order to fill apparent gaps is not permitted.