George Kubler and Martin Soria, in Art and Architecture of Spain and Portugal, trace the typology to the mid-15th century Aragonese "viril", a window in the high altar created to display the consecrated host.
In de Uranna's design, one passes from the oval nave through one of two doorways flanking the high altar.
It is made up of thin sheets of green marble from the Greek island of Tynos studded with seventy-two stars.
All of them constitute authentic jewels as they are studded with precious stones, except for seven that are located in the canopy carved in silver and with ivory applications.
[1] Capilla ó pieza que suele haber detras de un altar, donde se venera alguna Imágen.