The Last Guardian by David Gemmell
The gateway between past and present has opened, and evil forces of enormous power are unleashed. To close the gateway, the Sword of God must be found, and all that is known is that it shines in the clouds above the City of Beasts - a city ruled by the Dark Queen. Only one man can stand at the gateway of time - Jon Shannow, the Last Guardian. The hunters from his past who seek his death are but the first obstacle. For what Shannow doesn't know is that his actions could warp time itself - and herald the doom of worlds.