The same night King Harald and his men went to the house where Maria slept and carried her away by force. Then they went down to where the galleys of the Varings lay, took two of them and rowed out into Sjavid sound. When they came to the place where the iron chain is drawn across the sound, Harald told his men to stretch out at their oars in both galleys; but the men who were not rowing to run all to the stern of the galley, each with his luggage in his hand. The galleys thus ran up and lay on the iron chain. As soon as they stood fast on it, and would advance no farther, Harald ordered all the men to run forward into the bow. Then the galley, in which Harald was, balanced forwards and swung down over the chain; but the other, which remained fast athwart the chain, split in two, by which many men were lost; but some were taken up out of the sound. Thus Harald escaped out of Constantinople and sailed thence into the Black Sea...

From "Heimskringla; Or, The Chronicle of the Kings of Norway" by Snorri Sturluson (~1230) http://www.gutenberg.org/ebooks/598

They rowed as hard as they could at the chain, while everyone who wasn't rowing ran to the back of the longship, basically popping a wheelie, raising the prow of the ship. When the front passed over the chain they all ran to the fore of the ship and the chain slid along under the keel. Whether or not this actually happened . . . Norwegian viking site explaining the maneuver