The frontier-guarding soldiers really live 'a hundred battles in yellow sand, armor worn through.'
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From 王昌龄 (Tang) 从军行·其四: 黄沙百战穿金甲，不破楼兰终不还 ('in yellow sand, a hundred battles wear through golden armor; until Loulan falls, I will not return'). A frontier soldier's oath. 楼兰 (Loulan) was a Silk Road kingdom on the edge of the Taklamakan desert.
usage
穿 here = 'to wear through / to pierce', not 'to wear (clothes)'. 金甲 = gilded or bronzed armor. Almost always paired with 不破楼兰终不还.
