Up to this point the route had climbed very gradually westwards from London, but from here it changed into one with steeper gradients which, with the primitive locomotives available to Brunel, was better operated by types with smaller wheels better able to climb the hills. These gradients faced both directions, first dropping down through Wootton Bassett Junction to cross the River Avon, then climbing back up through Chippenham to the Box Tunnel before descending once more to regain the River Avon's valley which it followed to Bath and Bristol.[37]