Ruy Lopez, Modern Steinitz Defense

Algebraic notation identifies a6 as column a and row six. The Modern Steinitz Defense appears after Black plays a6, White’s bishop retreats to a4, and Black supports the e5-pawn with the d6-pawn. The central structure is solid because the pawns support each other, and the earlier a6 move allows Black to gain more space on the side where the queens began with b5 when appropriate.

The price of that solidity is reduced room for the black pieces. A restricted position is one in which several pieces have few useful squares. White commonly prepares c3 and d4 to challenge e5. Black brings out the g8-knight and f8-bishop, then looks for the right moment to exchange or counterattack in the center.

The word Modern distinguishes this line from the direct Steinitz Defense, where Black plays d6 without inserting a6 and the bishop retreat first. The move a6 creates extra options on the side where the queens began, but it also spends a move. The comparison therefore depends on both the pawn structure and the move order used to reach it.