Pedro Cieza de León was a Spanish soldier who arrived in South America as a teenager and spent roughly two decades traveling through the recently conquered Inca territories, eventually writing the Crónica del Perú (Chronicle of Peru), published in 1553 — one of the earliest and most historiographically respected Spanish accounts of the region, notable among his contemporaries for actually attempting to weigh and cross-check the oral traditions he recorded rather than simply repeating rumour uncritically.
Cieza de León is explicit that he did not personally witness the giants he describes — he states directly that he is relaying a tradition told to him by the Manta people, an indigenous group inhabiting the coastal area north of the Bay of Guayaquil, in what is now Ecuador, who in turn attributed the story to their own distant ancestors.