Although the commemoration of the apostle Thomas is a relatively late development in the Western calendars, the feast-day lends itself for a comparative study of the liturgical commemoration and the apocryphal Acts of Thomas. In this comparative research, the Old Hispanic rite surfaces as the domain where liturgical prayers borrow from the apocryphal texts most frequently. While the Acts of Thomas, transmitted in the Latin Passio Thomae (BHL 8136) and De miraculis beati Thomae apostoli (BHL 8140), deal extensively with the apostle’s preaching of a chaste, almost encratitic way of life, the liturgical prayers in the Hispanic sources concentrate on a less well known episode in the first part of the Passio Thomae, where Thomas performs his mission disguised as a court architect for rex Gundafor. The ‘spiritual edifice’ (spiritale edificium) that is the result of this assignment is central in the Old Hispanic Mass orders for Thomas. The prayers highlight the transformation of the civitates Indorum into Christian communities, as well as the transfer of their destination from a terrestrial to the celestial regnum, of which Gundafor’s palace is the typus.