It is named after the famous 18th century player François-André Danican Philidor, who advocated it as an alternative to the common 2…Nc6. Today it is known for being a solid, but rather passive, opening for black. It is rarely seen in top level play. Philidor’s main idea behind the move 2…d6 was of course to protect the e-pawn, but most importantly to prepare immediate f7-f5 pawn push, attacking White’s e4 pawn. Since white already placed its knight on f3, the f2-pawn cannot be used to protect the e-pawn which makes Black’s idea possible.