The Philidor Defence traditionally began with the moves 1.e4 e5 2.Nf3 d6, but times have changed considerably. With this move order it was found that if Black plays 3…Nd7 to strongpoint e5, then after 4.Bc4 he finds it difficult to continue his development without making some concession. As an example 4…Ngf6 is met by 5.dxe5 dxe5 (5…Nxe5 6.Nxe5 will win the f7 pawn) 6.Ng5, 4…Be7 is bad because of 5.dxe5 Nxe5 (5…dxe5 6.Qd5) 6.Nxe5 dxe5 7.Qh5 and 4…c6 5.O-O Be7 6.dxe5 dxe5 7.Ng5 Bxg5 8.Qh5 Qe7 9.Qxg5 gets the two bishops.
This led to a new move order for Black, namely 1.e4 d6 2.d4 Nf6 3.Nc3 e5, and now after 4.Nf3 Nbd7 5.Bc4 Be7, when Black achieves the Hanham setup that he’s been aiming for. White can also opt for an endgame with 4.dxe5, but this is not thought to be too dangerous, 4.Nf3 Nbd7 5.g4!? is probably more worrisome.
A number of strong players can be found on the Black side of this line, for example Maxime Vachier Lagrave, Baadur Jobava, Victor Bologan and Pavel Eljanov. Here’s one of MVL’s wins in this line: