Short answers, pulled from the story.
The Battle of the Teutoburg Forest was a decisive ambush fought between 8 and the 11th of September 9 CE in which a Germanic coalition destroyed three Roman legions led by Publius Quinctilius Varus. The Germanic alliance was commanded by Arminius of the Cherusci tribe. Roman casualties have been estimated at fifteen thousand to twenty thousand dead.
Arminius was a Cherusci chieftain who had been taken hostage by Rome around 8 BCE as a child and received a Roman military education. He rose to command Roman auxiliaries before returning to Germania and secretly building a coalition of Germanic tribes. He exploited his position as Varus's trusted advisor to lure the Roman column into narrow forested terrain near Kalkriese Hill, where the Germanic forces had prepared earthen walls, trenches, and ambush positions that negated Rome's tactical advantages.
The battle is now associated with the area around Kalkriese, a village on the north slopes of the Wiehen hills in Lower Saxony, about one hundred kilometres northwest of Bielefeld. The identification was triggered in 1987 when British amateur archaeologist Tony Clunn found Augustan-era coins and Roman sling bolts there with a metal detector. Excavations since then have revealed battle debris along a corridor almost twenty-four kilometres long.
The three legion numbers XVII, XVIII, and XIX were retired and never used again by the Romans, a distinction not applied to other legions that suffered defeat. Three replacement legions, Legio II Augusta, XX Valeria Victrix, and XIII Gemina, were sent to the Rhine. The legionary eagles of all three lost legions were eventually recovered: one from the Marsi in 14 AD, the XIX Eagle from the Bructeri in 15 AD, and the last from the Chauci in 41 AD.
The battle effectively ended Roman efforts to expand beyond the Rhine. The Rhine became a permanent border between the Roman Empire and independent Germania, and Rome made no major incursion into the region until the Marcomannic Wars under Marcus Aurelius in the reign of 161-180 AD. Logistical and economic factors reinforced the decision: northern Germania was less developed, offered little tribute, and was far harder to supply than territories accessible via the Rhine.
After Tacitus's works were rediscovered in the 15th century, Arminius was recast as "Hermann" and became a symbol of pan-German identity. A monument to Hermann, the Hermannsdenkmal, was begun in 1841 near Detmold on the summit of Grotenburg and completed in 1875 following the Franco-Prussian War that unified Germany. The statue faces west toward France, reflecting the national rivalry of that era.