The Battle of the Teutoburg Forest.

2000 years ago, between 9 - 11 September the battle of the Teutoburg Forest took place. It was one of the greatest Roman army disaster. Three legions, many cohorts of auxilary troops and squadrons of cavalry were destroyed in that battle against the alliance of the Germanic tribes. Around 15000 - 20000 Roman soldiers died including their commander P. Quinctilius Varrus. According to Suetonius, upon hearing of the defeat, the Emperor Augustus repeatedly shouting: "Quintili Vare, legiones redde!" (Quintilius Varus, give me back my legions!).
More details about the battle are in this article from Wikipedia.

A few years ago I found on the internet this poem about the battle. Unfortunately I don't remember the author.

Deep in the forest the legions are lost!

"The clamor of armor and brass,
the joyful perfection of youth and geometry,
of order and open space, is muffled beneath
the obscure chaos of indifferent branches
and enveloping gloom: deep in the forest,
the legions are lost.

How young we were,
and glorious, when in the full sun of
Roman days, we sought an Empire of Reason,
rather than a reason for Empire.
How old we are now, with arms too leaden
to embrace either a man or an ideal.

The forest is inscrutable, and whispers
the foreign words of wind through insensible leaves.
An occasional messenger, lame and thin,
brings news of battles, but in another place,
sometime already past.

His eyes are filled
with shadows. He says little we do not already know:
Deep in the forest, the legions are lost."