On each side, above and below the bridge, at a moderate distance--a bow shot--was anchored a heavy, raft floating upon empty barrels.

Each raft was composed of heavy timbers, bound together in bunches of three, the spaces between being connected by ships' masts and lighter spar-work, and with a tooth-like projection along the whole outer edge, formed of strong rafters, pointed and armed with sharp prongs and hooks of iron.

Thus a serried phalanx, as it were, of spears stood ever on guard to protect the precious inner structure.

Vessels coming from Zeeland or Antwerp, and the floating ice-masses, which were almost as formidable, were obliged to make their first attack upon these dangerous outer defences.

Each raft; floating in the middle of the stream, extended twelve hundred, and fifty-two feet across, thus protecting the whole of the bridge of boats and a portion of that resting upon piles.
Such was the famous bridge of Parma.