How was Doward destroyed?

From the text:

Ambrosius besieged the place in the conventional way for about three days. Where he could, he drew up siege engines and tried to break the defenses. He did indeed breach the outer rampart in two places above what was still called Ro mans’ Way, but when he found himself stopped by the inner . rampart and his troops exposed to the defenders, he withdrew. When he saw how long the siege would take, and how, even in the three days, some of his British troops quietly left him and went off on their own, like hounds after the rumour of Saxon hares, he decided to make an end quickly. He sent a man to Vortigern with conditions for surrender.. Vortigern, who must have seen the defection of some of the British troops, and who well understood Ambrosius’ position, laughed, and sent back the messenger without a message, but with the man’s own two hands severed, and bound in a bloody cloth to the belt at his waist.