I've read almost all of the CASCA books and this is one of the few series that I have read over and over many many and many times - hard to come by and demands a very high resale price on Amazon Dot Com in case you ever come across them.
In essence CASCA was the Roman Soldier at the crucifixion of the Christ who 'hastens' the death process using his spear. The Christ said to him "as you are now so shall ye be until my return - a soldier for hire". So starts his 2,000 year journey for Casca the Mercenary. The writing for the time period being told is historically factual in terms of weapons used, event that occurred, battles fought, customs of the place and time. All tongue and check in that it's just another dime store pulp storybook...but they sure are fun to read (and re-read!).
The series are 120 to 160 pages and are all easy reads.
This story takes place in Africa circa late 1960's early 1970's - get into a African Nation, bump off it's leader, Matthew Dzhombe, the dictator of Kimshakaand then get out as best as they can. Story is along the lines of the movie "The Wild Geese". Lots of action.
Casca - Casca Longinus aka Casey Romain in the modern period - The Eternal Mercenary. Series written by (SGT) Barry Sadler (of Vietnam Green Beret fame/album). Wrote (most of) the series prior to his death. Like the Conan character by Robert E. Howard, other authors have stepped up to continue the character of Casca and his journey.
Casca, condemned to a life of a mercenary by the Christ, and until the return of The Christ he was bidden to walk the face of the earth and know no rest, and to be just who he was: a mercenary, soldier for hire!
He cannot be killed, but he can feel every knife blade that enters his body, every bullet that penetrate his skin, every bomb blast, and pain is still pain.
He has lived for 2,000 years. A Roman soldier in Jedea during the time of Christ. A Germain Soldier on the Russian Front during WWII. A Foreign Legionaire in Vietnam during the last days of the French Occupation during the mid 1950's. A Barbery Pirate, a member of a Japanese Warlords army where he earlier found out that he couldn't drown, but that water in his lungs was like breathing fire. An american soldier in Vietnam during the mid-1960's.
Washed upon the shores of the Mayan lands in circa 1300 AD were he had his heart cut out by the sun priest and Casca reached up and took his beating heart and put it back into his own open chest, and all say it close up by its own accord and watched as Casca walked down the temple steps and into the crowd on onlookers - none dared to touch him.