Explanation: When Julius Caesar was sieging the Gallic fortified town of Alesia, he built two walls - one to keep the Gauls in Alesia, in Alesia; and one to keep Gallic reinforcements out of his camp, leaving the Romans nestled between the two armies. A siege within a siege!

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Yo dawg. I heard you liked walls. So we put a wall behind yo wall so you can siege while being sieged.