The theory of the Ruy Lopez is the most extensively developed of all Open Games, with some lines having been analysed well beyond move thirty. At nearly every move there are many reasonable alternatives, and most have been deeply explored. It is convenient to divide the possibilities into two groups based on whether or not Black responds with (3...a6), named the Morphy Defence after Paul Morphy, although he was not the originator of the line. The variations with Black moves other than 3...a6 are older and generally simpler, but the Morphy Defence lines are more commonly played.