Trojans pounded down on them!
Tight formations led by Hector careering breakneck on
like a deadly rolling boulder torn from a rock face —
a river swollen with snow has wrenched it from its socket,
immense floods breaking the bank’s grip, and the reckless boulder
bounding high, flying with timber rumbling under it,
nothing can stop it now, hurtling on undaunted
down, down till it hits the level plain
and then it rolls no more for all its wild rush.

Homer (fl. 7th-8th C. BC) Greek author
The Iliad [Ἰλιάς], Book 13, l. 136ff (13.136) (c. 750 BC) [tr. Fagles (1990), ll. 162-70]

Cowper notes "The following simile is considered by critics as one of the finest in Homer." Alt. trans.:

Troy charged the first, and Hector first of Troy.
As from some mountain's craggy forehead torn,
A rock's round fragment flies with fury borne,
Which from the stubborn stone a torrent rends,
Precipitate the ponderous mass descends:
From steep to steep the rolling ruin bounds;
At every shock the crackling wood resounds;
Still gathering force, it smokes; and, urged amain,
Whirls, leaps, and thunders down, impetuous to the plain:
There stops -- So Hector. Their whole force he proved,
Resistless when he raged, and, when he stopped, unmoved.
[tr. Pope (1715-20)]

The powers of Ilium gave the first assault
Embattled close; them Hector led himself
Right on, impetuous as a rolling rock
Destructive; torn by torrent waters off
From its old lodgment on the mountain’s brow,
It bounds, it shoots away; the crashing wood
Falls under it; impediment or check
None stays its fury, till the level found,
There, settling by degrees, it rolls no more.
[tr. Cowper (1791), ll. 168-76]

But the combined Trojans first made the attack, and impetuous Hector first rushed against them: as a destructively-rolling stone from a rock, which a wintry torrent drives down the brow, having burst with a mighty shower the stays of the rugged rock, and bounding along, it rolls, and the forest resounds beneath it: but straightway it runs on uninterruptedly until it reach the plain, but then it rolls no longer, though impelled.
[tr. Buckley (1860)]

On pour’d the Trojan masses; in the van
Hector straight forward urg’d his furious course.
As some huge boulder, from its rocky bed
Detach’d, and by the wintry torrent’s force
Hurl’d down the cliff’s steep face, when constant rains
The massive rock’s firm hold have undermin’d;
With giant bounds it flies; the crashing wood
Resounds beneath it; still it hurries on,
Until, arriving at the level plain,
Its headlong impulse check’d, it rolls no more.
[tr. Derby (1864)]

Then the Trojans drave forward in close array, and Hector led them, pressing straight onwards, like a rolling rock from a cliff, that the winter-swollen water thrusteth from the crest of a hill, having broken the foundations of the stubborn rock with its wondrous flood; leaping aloft it flies, and the wood echoes under it, and unstayed it runs its course, till it reaches the level plain, and then it rolls no more for all its eagerness.
[tr. Leaf/Lang/Myers (1891)]

The Trojans advanced in a dense body, with Hector at their head pressing right on as a rock that comes thundering down the side of some mountain from whose brow the winter torrents have torn it; the foundations of the dull thing have been loosened by floods of rain, and as it bounds headlong on its way it sets the whole forest in an uproar; it swerves neither to right nor left till it reaches level ground, but then for all its fury it can go no further.
[tr. Butler (1898)]

Then the Trojans drave forward in close throng and Hector led them, pressing ever forward, like a boulder from a cliff that a river swollen by winter rains thrusteth from the brow of a hill, when it has burst with its wondrous flood the foundations of the ruthless stone; high aloft it leapeth, as it flies, and the woods resound beneath it, and it speedeth on its course and is not stayed until it reacheth the level plain, but then it rolleth no more for all its eagerness.
[tr. Murray (1924)]

The Trojans came down on them in a pack, and Hektor led them raging straightforward, like a great rolling stone from a rock face that a river swollen with winter rain has wrenched from its socket and with immense washing broken the hold of the unwilling rock face; the springing boulder flies on, and the forest thunders beneath it; and the stone runs unwavering on a strong course, till it reaches the flat land, then rolls no longer for all its onrush.
[tr. Lattimore (1951)]

Trojans massed and running charged them now, with Hector in the lead in furious impetus, like a boulder a river high with storm has torn away from a jutting bank by washing out what held it; then the brute stone upon the flood goes tossed and tumbling, and the brush gives way, crashing before it. It must roll unchecked as far as level ground, then roll no more.
[tr. Fitzgerald (1974)]

Then in a throng charged forward the Trojans, and Hektor was leading, avidly pressing ahead, as a rock rolls down from a cliff, thrust off of the crest of a hill when a river with winter rains swollen breaks with a marvelous deluge the pitiless cliff's foundation; bounding aloft it is flying along, and beneath it the woods are crashing, and it speeds ever unswerving until at the level plain it arrives, then rolls no longer for all of its onrush.
[tr. Merrill (2007)]