There is a lesson here

But the resistance of the garrison informed the Barbarians, that in the attack of regular fortifications, the efforts of unskillful courage are seldom effectual. Their general acknowledged his error, raised the siege, declared that "he was at peace with stone walls," and revenged his disappointment on the adjacent country.

-- History of the Decline and Fall of the Roman Empire, Vol 2, Chapter XXVI, Edward Gibbon