Early in recorded history, there are records of dogs being trained for the purpose of attacking a target. One of the most well-recorded ancient uses was in a battle between the Athenians and Corinthians, in which dogs were used to keep watch over a fortress and despite being unsuccessful in opposing an enemy attack, were able to alert the sleeping soldiers to the attack. Ancient Romans first adopted the use of dogs as a weapon after hordes of dogs delayed their victory in the Battle of Vercellae. The Romans not only trained them to attack, but also bred their attack dogs for ferocity. The effect of this was documented by Roman naturalist and writer Pliny the Elder, who wrote that the animals would not back down, even when confronted by swords. The Roman attack dogs were given metal armour covered in razor-sharp spikes, designed to force the enemy out of formation.