What is the first all iron building in the world?

The first all-iron building in the world is the Crumlin Viaduct in Wales, completed in 1857. Designed by engineer John Fowler, it was a pioneering structure that utilized cast iron for its entire framework. This innovative use of iron set the stage for future architectural advancements, showcasing the material's potential in construction. The viaduct remains a significant example of early iron architecture.