Following the failed Paraguayan counterattack at the Battle of Estero Bellaco, the Brazilian, Argentine, and Uruguayan invasion force continued their march into Paraguay and reached Tuyutí in the southwest corner of the South American nation. Paraguayan president Francisco López ordered another suprise attack and in what might be the bloodiest encounter ever fought in South America were completely defeated before the Allied entrenchments supported with extensive artillery positions. Estimated Paraguayan casualties numbered around 13,000, or more than half their force, with 6,000 of these dead. The defenders lost around a thousand killed. (By John Osborne)
"Paraguay," The American Cyclopedia and Register of Important Events of the Year 1866 (New York: D. Appleton and Company, 1873), 610.