Board Position
An old but solid King's Pawn defence, named after Andre Danican Philidor (the greatest player of the 18th century and one of its chief exponents).
Black leaves the "Épine Dorsale" to reply 2..P-Q3(d6) in move 2 (left). The straightforward but passive (and sometimes cramped) nature of this defence does however give White some ground in the centre. Other more subtle defences that deny White an immediate 3.P-Q4 opportunity are more popular.
Board Position
With careful play White has the better (more mobile) game, as Black's King's Bishop becomes shut in after move 7 (remaining so, as seen by move 10w, right). Variations include Legall's Mate and a famous "Opera Box Game" (Paris, 1858) between Morphy and Brunswick/Isouard.
Begin or Clear or Groups or see move: 1 e4 e5 2 Nf3 d6
for 3 d4 to (Hanham V:) 3..Nd7 4 Bc4 c6 5 0-0 Be7 6 Nc3 h6 7 a4 Ngf6 8 Qe2 0-0 9 Bb3 Qc7 10 h3
(Jaenisch C/A:) 3..Nf6 4 Nc3 Nbd7 5 Bc4 Be7 6 0-0 0-0 7 Qe2 c6 8 a4 h6