The stone extracted from the quarry in average size pieces was transported to the church in construction. When they were building one row, the master builder indicated to the stonemason the ashlar dimensions and probably the sign to be inscribed in it. The basic tools of the stonemason were the square, compass and peak. Once finished the work, the stone was placed in the row at the most convenient position to maintain the polished and marked face on the front face of the wall. Each stone has only one sign, rarely two, and it is placed in sight. This explains that the signs appear in normal or inverted position. The stonemason performs his work with a chisel and compass or by hand and, in some cases, with templates for the main form of the sign. The quality of the stone and the good polishing increases the quality of the signs. They have variants of its basic form according to the church, the geographical area, belonging to one or another order… without modifying their meaning.
Read more in The stonemason’s signs in the Romanesque churches in Spain.