Maybe you need two monopolies from a category to make a corporation, but a monopoly gets something at guilds or so.. you can have a monopoly in the ancient era. Like the world famous champagne wine, or Damascus steel, or Ming vases. Maybe not the best examples but you see what I am talking about? Maybe a unique luxury from luxury companies, Unique unit from strategic company, buildings from a bonus company Company from a monopoly, corporation from incorporating companies.