Harry Turtledove 
Golden Shrine 

Glaciers once covered the world with ice. Now a gap has opened in the ice wall. And through that gap come the men who call themselves "Rulers".Their cavalry rides on mammoths. Their bows can shoot faster, harder, farther. Their wizards wield power that neither the shamans of the Bizogots nor the wizards of Raumsdalian Empire can match, a magic that can melt the stone beneath a man’s feet and call down fire from the sky. Scattered Bizogot survivors hide. The Empire is shattered. The feckless Emperor is in hiding.Against the Rulers stands Count Hamnet Thyssen and a few friends: Jarl Trasamund of the Three Tusk Bizogots, the adventurer Ulric Skakki, and, most important, Marcovefa, the female shaman who has magic that Rulers cannot counter.Perhaps Hamnet and his allies can save their lands from Rulers. But first they must seek the legendary Golden Shrine – which has not been seen by human eyes since before the glaciers came.