Tumbo A - Tumbo A detail

It is one of the most prominent and outstanding medieval cartularies from the Iberian Peninsula, and one of the best records of the development of Santiago Cathedral from its origins to the 13th century.

During the tenure of Archbishop Gelmírez, work began on the cartulary known as the "Tumbo," with its 71 sheets of parchment containing the most important documentation about the cathedral, in chronological order. The first 40 sheets are from the original edition, and the rest were added later.

After the introductory prologue, the first part of the volume features a miniature depicting the "Inventio." This is the Latin name for the discovery of Saint James the Apostle's body "in Arcis Marmoricis" (meaning "in a marble tomb under arches"), in the primitive diocese of Iria Flavia during the tenure of Bishop Theodemar. This event marked the emergence of the cult of Saint James in the north of the Peninsula.

Alongside this miniature are images of monarchs and key figures in Leonese and Galician royalty of the period.