The ongoing Ychsma Project aims to shed light on the chronology and function of the late Prehispanic period at the well-known archaeological site of Pachacamac, Peru, through extensive archaeological research. The Temple of the Monkey is a special building that has been cleared, mapped, and excavated within the general framework of the study of “pyramids with ramps,” the most common form of monumental architecture at the site. Through the application of radiocarbon measurements, it can be shown that the temple has been used for around 150 yr and therefore is quite different from other pyramids with ramps previously studied (see Michczyński et al. 2003). Details of the temple, 14C sample selection, and methodology, as well as results, are discussed in this paper. The research has allowed us to make significant advances in the current understanding of pyramids with ramps and the function of the site of Pachacamac as a whole.