Cueva del Castillo was discovered in 1903 by Hermilio Alcalde del Río, a Spanish archaeologist, who was one of the pioneers in the study of the earliest cave paintings of Cantabria. The entrance to the cave was smaller in the past and has been enlarged as a result of archaeological excavations. Alcalde del Río found an extensive sequence of images executed in charcoal and red ochre on the walls and ceilings of multiple caverns.[citation needed] The paintings and numerous markings and graffiti span from the Lower Paleolithic to the Bronze Age, and even into the Middle Ages.[citation needed] There are over 150 depictions already catalogued, including those that emphasize the engravings of a few deer, complete with shadowing.[citation needed]