Robert Adams certainly was quite a prolific writer before he passed away around 1988, the year his last of his Horseclans novels was published – Number 18. (Plus two anthologies w/ "Friends of the Horseclans" where he let other writers try their hand at the fictional world he had created). He was one of the few mainstream authors that had a regular element of muscular Amazons in his stories, especially those involving the Bili the Axe character – who incidently was married to one of them.

In many ways, he was the Edgar Rice Burroughs of his day, even to focusing on the female characters as primary elements to the story, rather then as backdrop support to the male ones. The "Castaways in Time" series, as Alt-History, were interesting, fast moving reads, too.

“I like a good story well told. That is the reason I am sometimes forced to tell them myself.”
~ Mark Twain / Samuel Clemens (1907)