In 1968 J.R.R. Tolkien wrote a letter to his son Michael (The Letters of J.R.R. Tolkien #306) in which he describes a 1911 hiking trip in Switzerland which was the inspiration for some scenes in The Hobbit. He tells of an incident when he was hiking on a trail across a slope where melting snow had exposed a number of boulders, some of which began rolling down the slope and across his trail. He says
The quotes (or “inverted commas” as I think they’re charmingly known in Britain) around “hard pounding” are in the original. This makes me think Tolkien was referring to something specific; either a well known British saying or a literary reference. Does anyone know more about this? Googling the phrase turns up mostly pornography sites, which is probably not what Tolkien had in mind.
More specifically, a style of artillery fire relying on sheer volume of ammunition rather than precise targeting or other technical advantages. From the 1910 Encyclopedia Britannica:
Presumably Tolkien’s point was that all these boulders shooting across their path were like a bombardment.