Dulce et decorum est pro patria mori
Dulce et decorum est pro patria mori is a line from the Roman lyrical poet Horace's Odes (III.2.13). The line can be roughly translated into English as: "It is sweet and glorious to die for one's country."
As a consequence of Wilfred Owen incorporating the phrase into his similarly titled poem, "Dulce et Decorum Est", it is now often referred to as "the Old Lie"; see below.