Cassandra and the Trojan Horse, as it's being taken in to the city, sealing Troy's doom. From the Casa del Menandro in Pompeii.
The passage below comes from the Odysses - this is how Homer have the Phaeacians bard sing about the fall of Troy;
"For the Trojans themselves had drawn the horse into their fortress, and it stood there while they sat in council round it, and were in three minds as to what they should do. Some were for breaking it up then and there; others would have it dragged to the top of the rock on which the fortress stood, and then thrown down the precipice; while yet others were for letting it remain as an offering and propitiation for the gods. And this was how they settled it in the end, for the city was doomed when it took in that horse, within which were all the bravest of the Argives waiting to bring death and destruction on the Trojans. Anon he sang how the sons of the Achaeans issued from the horse, and sacked the town, breaking out from their ambuscade. He sang how they over ran the city hither and thither and ravaged it, and how Ulysses went raging like Mars along with Menelaus to the house of Deiphobus. It was there that the fight raged most furiously, nevertheless by Minerva's help he was victorious."
Homer - The Odyssey VIII
Translated by S. Butler 1898