It is part of group of religious buildings that include the Royal Church, and originally built by the Visigoths in the 7th century, in the form of a Greek cross.

[1] Based on historical accounts, and oral tradition, the site of the chapel was (around 560 A.D.) the location of a small Roman villa and, likely, a temple dedicated to the god Asclepius.

[2] In 656, Fructuosus of Braga, then Bishop of Bracara, founded on this site the Monastery of São Salvador, ordering the construction of the chapel, as his tomb.

[2] The architect followed the original hypothesis that the chapel was ordered constructed by Fructuosus of Braga as his 6th century tomb, following a model/design aesthetic based on the mausoleum Galla Placidia in Ravenna.

[2] The chapel of São Frutuoso continues to be an enigma, but it is a uniquely rare example of Visigothic structures in Portugal, based on a Greek-cross, which may have followed the design of a Byzantine mausoleum comparable to the Galla Placidia, in Ravenna.

The collateral façades are decorated with blind arcades, alternating between angular and double rounded-frieses, which are repeated in the tower cupola, and intersected by small round windows.

In northern part of the eastern arm of the chapel is an arcosolium, where the mortel remains of Saint Fructuosus was originally entombed, and exposed to the exterior.