Procopius, History of the Wars
5.21.19-22 (Gothic War, tr. H.B. Dewing):
And outside the gates they placed "wolves [λύκους]," which they make in the following manner. They set up two timbers which reach from the ground to the battlements; then they fit together beams which have been mortised to one another, placing some upright and others crosswise, so that the spaces between the intersections appear as a succession of holes. And from every joint there projects a kind of beak, which resembles very closely a thick goad. Then they fasten the cross-beams to the two upright timbers, beginning at the top and letting them extend half way down, and then lean the timbers back against the gates. And whenever the enemy come up near them, those above lay hold of the ends of the timbers and push, and these, falling suddenly upon the assailants, easily kill with the projecting beaks as many as they may catch.
Pat Southern and Karen Ramsey Dixon, The Late Roman Army
(New Haven: Yale University Press, 1996), p. 164:
This was a form of spiked drawbridge, which was dropped by the besieged on to attacking troops.