This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

Among Richmond's most interesting architectural features is its Cast-iron architecture. Second only to New Orleans in its concentration of cast iron work, the city is home to a unique collection of cast iron porches, balconies, fences, and finials. Richmond's position as a center of iron production helped to fuel its popularity within the city. At the height of production in the 1890, 25 foundries operated in the city employing nearly 3,500 metal workers. This number is seven times the number of general construction workers being employed in Richmond at the time which illustrates the importance of its iron exports. Porches and fences in urban neighborhoods such as Jackson Ward, Church Hill, and Monroe Ward are particularly elaborate, often featuring ornate iron casts never replicated outside of Richmond. In some cases cast were made for a single residential or commercial application.
What United States city has the most cast iron architecture?