The epigraphic pieces, crafted from white limestone, hold the highest historical and artistic value in the museum.

Piece 1 relates to the restoration of the temple and marks the first mention of Adefonsus Confessus. It highlights his efforts to restore and dignify the damaged temple of San Martín as a pious act dedicated to the Lord.

Piece 2 refers to the consecration of the temple. It not only provides the date of restoration (October 12, 951) but also includes a list of the holy relics deposited in the temple according to early medieval liturgy. Among these relics are those of Saint Salvador (the Saviour), Holy Mary, and Saint Martin, the miracle-working bishop to whom the church is dedicated and who was greatly venerated during the High Middle Ages in Asturias.

Piece 3 is an intriguing example of early medieval funerary customs: it is the epitaph of Adefonsus Confessus, dating from July 27, 969. In it, the founder expresses his desire to be buried in the church he had honored and urges the faithful to pray for the spiritual well-being of his soul.