The work was completed in 1609 or 1610, and on 14 July 1610 the church was consecrated. It was built in the form of a Latin cross with a series of shallow domes in the vault over the nave and a large dome over the crossing, with a semi-dome over the apse. The following day, on Sunday 15 July 1610 (the feast of Santiago) the altarpiece or "retablo" behind the high altar was inaugurated. This sumptuous structure was arranged in four registers with an apex. It was decorated with 14 paintings by the celebrated Basque painter Baltasar de Echave Orio (who is also credited with designing the "retablo"), alternating with carved wooden statues standing in niches. At the centre of the second register, directly above the later neo-classic ciborium (presumptively installed in the first decades of the 19th century and visible in a 19th century lithograph which shows the arrangement of the "retablo"), was a carved and painted panel in high relief of the patron saint of the church, Santiago Matamoros, the only part of the "retablo" that has survived. Torquemada applauded the skill of the Indian craftsmen and singled out for praise one of those who worked on the "retablo", Miguel Mauricio, calling him an artist second to none among the Spanish.