History sometimes imprints itself on music and then slips away, leaving only its impression, like a calling card. Thanks to French soldiers threatening Vienna more than 200 years ago, we heard on Thursday night in Symphony Hall the martial drum rolls of the ­Agnus Dei in Haydn’s “Mass in Time of War.”

In other words, the composer did not need posterity as muse; he had current events. Napoleon’s spectacular string of military victories in 1796 prompted Austria to press its composers into the service of rallying spirits at home.