As alluded, the walls stood the test of time (1,000 years) until the final siege in 1453. The Ottomans fired thousands of cannon shots (weighing 1k lbs) into the walls and ultimately broke through.
I'm struck by the significance. The walls allowed the Byzantine Empire to outlive the Roman Empire by ten centuries. Their undoing marked the end of medieval times (the collapse of the Western Roman Empire marked the start).
Fun fact about that cannon: it took so long for the cannon to cool off between shots that the Byzantines were able to patch each hole it caused before the next shot.
The repairs to the walls under the Ottoman cannon fire made use of the rubble, they made a wooden "basket" to hold the rubble; this ended up being very effective, as just like sand, the slight "give" to the rubble swallowed up much of the force of the cannonball.
I'm struck by the significance. The walls allowed the Byzantine Empire to outlive the Roman Empire by ten centuries. Their undoing marked the end of medieval times (the collapse of the Western Roman Empire marked the start).