The Conquistador by Barry Sadler (Casca Series, Book 10) from Books In Motion.com

Casca Longinus: Cursed by Christ on Golgotha, condemned to outlive the ages, wandering the globe as a constant soldier. Forever fighting, surviving, and waiting for Him to return. Now Casca is in Sixteenth Century Mexico where enemies of the majestic Aztec King Montezuma are sacrificed to his bloodthirsty gods by the thousands. Traveling in the party of Spanish Conquistador, Hernan Cortes, Casca (as Carlos Romano)returns to the savage land seeking revenge against the ritual priests who once ripped his very heart from his chest.