The most popular alternatives to 2.Nf3 are the Vienna Game (2.Nc3), the Bishop's Opening (2.Bc4), and the King's Gambit (2.f4). These openings have some similarities with each other, in particular the Bishop's Opening frequently transposes to variations of the Vienna Game. The King's Gambit was extremely popular in the 19th century. White sacrifices a pawn for quick development and to pull a black pawn out of the center. The Vienna Game also frequently features attacks on the Black center by means of a f2–f4 pawn advance.