As a simile for ‘ancient’ you could use a range of places and races, but here the intoning of the prayer makes ‘Jewish’ particularly appropriate.  In other contexts, we could say as ancient as China; as ancient as Babylon; as ancient as a trireme…

And he began intoning a prayer as ancient as the Jewish nation.

Source: Vasily Grossman, ‘In the Town of Berdichev’, The Road: Stories, Journalism, and Essays, trans. Robert and Elizabeth Chandler with Olga Mukovnikova, afterword Fyodor Guber (New York: New York Review Books, 2010), p. 19

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