These are structures of ladrillo located beside the Cagayan and Pinacanauan Rivers. They were built separately in the 18th century: one during the administration of Fr. Bernabe de la Magdalena, OP and another two during the administration of Fr. Antonio Lobato de Santo Tomás, OP (1765-94). It was used to manufacture ladrillos (red bricks) and lime for the construction of churches & other infrastructures during the Spanish era. Contrary to what others claim as forced labor, the laborers were paid by the authorities for their services. The hornos were also used for curing tobacco and for communications purposes.