Two sets of chains/fetters from the Roman Period that are on display in the Archaeological Museum in Lyon (ancient Ludgunum). They are made of iron and look very sturdy. They could be used to restrain prisoners and/or slaves.
"Chains" are mentioned over 20 times in the New Testament! For Example:
Acts 12:6 The night before Herod was to bring him to trial, Peter was sleeping between two soldiers, bound with two chains, and sentries stood guard at the entrance. 7 Suddenly an angel of the Lord appeared and a light shone in the cell. He struck Peter on the side and woke him up. “Quick, get up!” he said, and the chains fell off Peter’s wrists.
To view another example of "Chains/Fetters" Click Here.