The Second Severn Crossing, the bridge that links England and South East Wales over the River Severn, is marking its 20th anniversary.
The 5,128m (16,824ft) long structure took four years to build, cost £330m and was officially opened by Prince Charles on 5 June 1996.
Work began on the M4 crossing in 1992 after the original Severn Bridge, built three decades earlier, struggled to cope with the volume of traffic.
Due to erratic currents and a huge tidal range, many of the bridge's 2,000-tonne pier foundations had to be constructed onshore.
They were then shifted onto a large tracked vehicle - similar to those used to move space shuttles, loaded onto a barge and floated out on the high tide to the appropriate sites.
The crossing, which stretches between South Gloucestershire in England and Monmouthshire in Wales, now carries more traffic than its forerunner the Severn Bridge, which is still in use.
Sir John Armitt, who project managed the bridge's construction, said he still gets a thrill when he drives over it.
"Building a bridge like this is especially rewarding as you can see instantaneously the benefits it delivers," he said.
"One hundred years ago the only way to cross the lower Severn Estuary was by ferry. Today 80,000 vehicles safely cross the lower Severn every day."