history
From 辛弃疾《永遇乐·京口北固亭怀古》 (Xin Qiji, Yongyu Le: At Beigu Pavilion in Jingkou, Recalling Antiquity, 1205, Southern Song). Referring to 刘裕 (Liu Yu, founder of Liu Song, r. 420–422) who launched great northern campaigns from Jingkou: 想当年，金戈铁马，气吞万里如虎 (I think of those days - gold halberds and iron horses, a spirit that swallowed ten thousand li, like a tiger). Xin, a failed irredentist general-poet, is lamenting that the Southern Song has no Liu Yu to retake the lost north.
usage
Paired with 金戈铁马 ('gold halberds and iron horses' - also now a set idiom for martial glory). Xin Qiji's line has become the standard rhetorical flourish for any sweeping campaign - military, political, or commercial.
