Don't trust your enemies even if they show a friendly approach

An allusion to the story of the wooden horse of Troy, used by the Greeks to trick their way into the city. As narrated in Virgil's (70-10 B.C.) Aeneid (Book 2, 49), the Greeks, pretending to abandon the ten-year siege of Troy, built a huge hollow wooden horse and left it on the beach outside the city as a thank-offering to the Gods. The Trojans, thinking that the Greeks were gone, wanted to drag the horse inside the city walls, but the Trojan priest Laocoon, suspecting that some menace was hidden in the horse, warned the Trojans not to accept the gift, crying: @@©Equo ne credite, Teucri. Quidquid id est timeo Danaos et dona ferentes (Do not trust the horse, Trojans! Whatever it is, I fear the Greeks even when they bring gifts). Unfortunately, Laocoon was not believed and that night the soldiers hidden inside the horse, opened the city gates to the entire Greek army. As a result, Troy was sacked and destroyed.
In Medieval times, this phrase became a sententia, a veritable proverb cited by ecclesiastical writers.