In the 12th century BC, the Trojans made the biggest mistakes which their decline. At that time, the walls of the city of Troy were so high and strong, that the Greek army could not be get through it. So they planned a trick. They pretended to end the war and sent a large wooden horse to Troy as a gift which the Trojans accepted. At night, when everyone was asleep, the Greeks soldiers came out of the horse and opened the gates of the city, letting the Greek army in. As a result of this biggest mistakes, Troy was captured which ultimately led to the decline of this city.