The pawn chain base is the rearmost pawn in a pawn chain — a series of pawns protecting one another diagonally — and is structurally the most vulnerable link in that chain.
A pawn chain works because each pawn covers the one in front of it. Remove the base pawn — through a direct attack or an opponent’s pawn lever — and every pawn above it loses its support. For instance, in the white chain d4-e5 (typical of the French Defence), d4 is the base: if Black plays …c5 to challenge it, the entire chain is threatened at its foundation. Symmetrically, Black’s chain base is e6, which White targets with an advance such as f4-f5.
In practice, attacking the opponent’s chain base is a key strategic idea in closed and semi-closed positions. Identify each side’s base as soon as the pawn structure locks up: your plan will often involve undermining it with a lever, while defending your own base in return. Recognising the base early helps you build a coherent plan rather than moving pieces at random.