Castelvecchio, the oldest part of the Buonconsiglio complex, was built in the first half of the 13th century on a rocky hill against the eastern side of the city walls, near the Adige River. It originally served as a military fortress. It is still possible today to see evidence of its original purpose; the solid structure of the building, the external walls of hewn stone, defensive elements such as the embrasures, the ironclad Gothic door and the entrance built over the ancient drawbridge. The three rows of merlons visible on the façade mark the successive phases of adding storeys to the buildings (14th-15th centuries).
The presence of windows with Guelph crosses, and the Loggia above them, create an architectural elegance and underline the transition of the structure into a residence and less-so for defensive purposes.