More than 150 years after its creation, the original main line has been described by historian Steven Brindle as "one of the masterpieces of railway design".[53] Working westwards from Paddington, the line crosses the valley of the River Brent on Wharncliffe Viaduct and the River Thames on Maidenhead Railway Bridge, which at the time of construction was the largest span achieved by a brick arch bridge.[54] The line then continues through Sonning Cutting before reaching Reading[55] after which it crosses the Thames twice more, on Gatehampton and Moulsford bridges.[56] Between Chippenham and Bath is Box Tunnel, the longest railway tunnel driven by that time.[57] Several years later, the railway opened the even longer Severn Tunnel to carry a new line between England and Wales beneath the River Severn.[6]