The Gap (Harry Turtledove)

Count Hamnet Thyssen is a minor noble of the drowsy old Raumsdalian Empire. Its capital city, Nidaros, began as a mammoth hunters' camp at the edge of the great Glacier. But, that was centuries ago, and as everyone knows, it's the nature of the great Glacier to withdraw a few feet every year. Now Nidaros is an old and many-spired city; and though they still feel the breath of the great Glacier in every winter's winds, the ice cap itself has retreated...

Continuing the alternate-Bronze-Age epic begun in Harry Turtledove's Beyond the Gap: The glaciers came and covered the world with ice. Now they are in retreat. North of the city of Nidaros, north of the forest, north of the steppes where the nomadic Bizogots hunt, a gap has opened in the ice-wall. And down through that gap come the men who call themselves "Rulers." Their terrifying cavalry rides wooly mammoths. Their bows can shoot arrows farther...