Short answers, pulled from the story.
The Iron Bridge first spanned the River Severn on the 2nd of July 1779 before opening to public traffic on the 1st of January 1781. Construction began at a site adjacent to where a ferry had run between Madeley and Benthall with five sectional cast-iron ribs giving the bridge its span of 100 feet.
Thomas Farnolls Pritchard wrote to his friend John Wilkinson in 1773 suggesting a cast iron bridge that became the final design after other proposals failed. Construction began at a site adjacent to where a ferry had run between Madeley and Benthall with masonry and abutments constructed between 1777 and 1778 while ribs lifted into place during summer 1779.
Trustees closed it to vehicular traffic from the 18th of June 1934 because the metal deck was dangerously heavy so a weight limit of 4 tons was imposed initially. Housing boom of the 1930s meant drivers distributing tiles insisted on using the bridge which led to the decision to close it for safety reasons.
A wall was built in July 1783 to prevent the north bank from slipping into the river but cracks appeared in the stone land arch on the south side in December 1784 due to gorge instability. Over 20 landslides are recorded in the British Geological Survey's National Landslide Database for this area causing sides of the gorge to move towards the river forcing feet of the arch closer together.
The bridge became part of UNESCO Ironbridge Gorge World Heritage Site created in 1986 alongside adjacent settlement. It stands as Grade I listed building owned by Telford and Wrekin Council with recognition including designation as scheduled monument in 1934 plus International Civil Engineering Landmark status awarded 1979.