Source: YouTube video linked in OP
Transcription
EXTRA INFO:
The Romans were experts at fortifications and siege warfare.
Whenever a Roman army would camp for the night, a large part of the army would build a wooden fort which would usually be finished in a day. A Roman army on the march were described as “moving cities”.
One example is the Siege of Alesia where the Romans built a wall to trap the Gauls then built another wall to protect themselves from new Gallic reinforcements who came to break the Romans' siege.
It was a siege where the besiegers were sieged by both new besiegers and the besieged but the besiegers won the siege anyway.