Within the actions carried out by the Directorate General of Cultural Heritage of the Government of Aragon in relation to the judicial procedure on the pillage of the Celtiberian city of Aratis (Aranda de Moncayo, Zaragoza), a large area was located with several concentrations of tumular structures in the area of Penas Pasera, previously unpublished. It is a flat and elevated area, at a level similar to the upper part of the city and about 1300 m away. The peculiar morphology of a large tumular structure located at the highest level of this area, and its presumable relationship with the Celtiberian city, motivated its archaeoastronomical study. A detailed analysis has allowed to identify an important quantity of markers and visual landmarks that could be used to indicate and identify the most important dates of the Celtic calendar. This opens the door to various interpretations of the structure and of the large tumular group.