Martti Pärssinen, Denise Schaan and Alceu Ranzi (2009). "Pre-Columbian geometric earthworks in the upper Purús: a complex society in western Amazonia". Antiquity. 83 (322): 1084–1095. doi:10.1017/s0003598x00099373. S2CID55741813.
Martti Pärssinen, Denise Schaan and Alceu Ranzi (2009). "Pre-Columbian geometric earthworks in the upper Purús: a complex society in western Amazonia". Antiquity. 83 (322): 1084–1095. doi:10.1017/s0003598x00099373. S2CID55741813.