An acclaimed historical novelist (Sharpe's Triumph, 1999, etc.) casts a canny eye way, way back.
It's 2000 b.c., and the old ways—and the old gods—seem somehow less controlling than they used to be. Even Hengall, the once tyrannical chief in Ratharryn, appears unusually vulnerable, and his oldest son, sensing this, is on the point of challenging his authority. Hengall has three sons: Camaban, whom he’s ashamed of because he was born club-footed; Saban, whom he favors but who, at age 12, is a nonplayer, politically speaking, and Lengar, who is the tribe's great warrior and hunter. Obviously, then it’s the latter who will have to be killed if Hengall’s to stay alive. The power struggle mounts in intensity, complicated by the existence of nearby marauding bands in Cathalla and far-flung ones in Semennyn. And as men betray and murder each other, the wayward gods watch—ever in need of placating, usually by human sacrifice. Camaban, written off, startles all by becoming a first-class sorcerer-visionary and later point-man for a new religion, one that will award ascendancy to Slaol, the sun god, who in turn will end winter, eliminate death, and generate better behavior among humans. A new temple must be built in his honor, Camaban insists, the likes of which has never been seen before, a circle of magnificently massive stones and boulders—never mind that nothing of this description is indigenous to Ratharryn. Camaban has his way. Saban, the youngest of the brothers, grows old building a Slaol-worthy edifice; but when it’s finished, the men are still up to their old tricks: betrayal, murder, the usual.
Whatever the period, count on Cornwell to serve up the details on which verisimilitude thrives. Lots of that here, maybe more than required, but it's a sturdy story, too—an ancient sibling rivalry full of enough blood and thunder to hold anyone's interest.