Castling: when it is legal and why to move the king
Castling serves two purposes in one move: relocating the king and bringing a rook closer to useful play. A neat position behind pawns does not guarantee safety. First check whether the special move is legal, then assess how safe the king will be in its new location.
In this article
How the two pieces move
When White castles kingside, the king moves from e1 to g1 and the rook from h1 to f1. Queenside, the king goes to c1 and the a1 rook to d1. Black does the same on the eighth rank. In DUEL, select the king and its destination; the rook moves with it. Do not make a separate second rook move.
Check your castling rights
The king and participating rook must be on their original squares and must never have moved. Returning does not restore the right. No pieces may stand between them. The king cannot start in check, cross an attacked square or finish under attack. For queenside castling, b1 must be empty, but an attack on b1 alone does not prohibit castling: the king does not cross b1.
What our position shows
White has developed the f3 knight and c4 bishop. The f1 and g1 squares are empty and unattacked, so e1–g1 is legal. Pawns on f2, g2 and h2 remain in front of the king. The f1 rook does not yet attack the opponent, but can join the game more easily once the file opens. Development prepared this useful next step.
Do not castle automatically
A typical mistake is forgetting a bishop attacking a square the king crosses. Another is castling into an attack already underway and assuming safety is assured. Try “King safety”, then a bot game. Before castling, check three things: rights retained, path clear, no attacked king squares. Afterwards, keep watching the pawn shield.
Your move now.
Practise the idea on the board. You can make mistakes, try again and start over.
Open exerciseRules and sources
Use these links to check the rules and explore the topic further.