The reliefs from Itziar originally formed part of an altarpiece with three vertical sections in the general shape of an inverted "T". The Nativity stood in the centre section flanked by the scene of the Betrothal to its left and the Circumcision to its right.
Accordingly, the structure of the altarpiece was very similar to those of Rieden, Funchal and St. John the Baptist in Belmonte inasmuch as it too had a lattice border on the bottom: an element that was normally incorporated into altarpieces manufactured in Brussels that helps identify the origins of this particular work. Given that its style appears to date from somewhat later, the reliefs were probably covered by poligonally-shaped canopies like those on the relief of the Passion in Lekeitio.
The original structure was probably protected by four lateral wings: the two larger wings, one on either side of altarpiece's main body, protected the body itself, while the two smaller wings protected the part of the centre section that protruded from the level of the reliefs on either side.