of the builders or the building date. In 2005, a book was published in Spanish by Aparicio and Esteban titled The Pyramids of Güímar: Myth and Reality. Aparicio and Esteban suggest that the solstitial orientations of the pyramids were potentially motivated by the Masonic symbolism. These authors argue that solstices are very important in the symbolism of Freemasonry, and that the owner of the land in the epoch in which the pyramids were built was himself a Freemason. This motivation would be only an aesthetic one and would not modify in any rate the fundamental motivation (agriculture) and date of construction. Archaeological excavations Between 1991 and 1998, with the agreement of Thor Heyerdahl, multiple excavations of the site by archaeologists of the University of La Laguna (Departamento de Prehistoria, Antropología e Historia Antigua) took place. In 1996 the results of the 1991 excavation were presented at a colloquium (published in 1998), providing evidence for the dating of the pyramids. According to the preceding geophysical Georadar-Survey eight locations adjacent to the pyramids, each with an area of 25 m², were investigated in layers down to the solid lava-floor. In doing so it was possible to establish three specific sediment layers. Starting from the top these were: A layer of thickness averaging 20 cm, consisting of humus-rich earth with many plant remains and roots; tracks from ploughing were clearly identifiable as were a broad spectrum of readily datable finds from the second half of the 20th century. A layer of thickness averaging 25 cm, similar in composition to the first layer, however containing less humus and a larger amount of small stones; a large variety of finds which could be dated to the 19th and 20th century were found, of which an official seal from 1848 deserves particular mention. A layer of thickness between 25 and 150 cm, composed out of small volcanic rocks, most likely put in place in one movement, which levelled the uneven stone underneath; the stones contained only very few finds, mostly a small number of pottery shards, of which some was local and some imported, both kinds were roughly estimated as belonging to the 19th century; the pyramids stand stratigraphically directly on top of this bottom layer, therefore allowing only for an earliest date of construction of the pyramids within the 19th century. Furthermore, under the border edge of one of the pyramids, a natural lava cave