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The circle symbolizes the heaven.
The semicircle symbolizes the door of heaven.
The square symbolizes the earthly.
The eight symbolizes the resurrection.
Saint Bernard of Clairvaux write "The circle is Heaven (the house of God), a body rests on their feet (the pillars) every Temple must move from Earth to Heaven passing from square to the circle -
Churches:
Santa María de Nieva (Segovia), Puilampa (Zaragoza), Santa María de Eunate (Navarra), Torres del Río (Navarra), Capilla de Santa Lucía Catedral de Barcelona, Santa María de Poblet (Tarragona), Santa María de Huerta (Soria), Vilar de Donas (Lugo).
Read more in The stonemason’s signs in the Romanesque churches in Spain.