The Greek writer Herodotus in his Histories, records several pontoon bridges.
The Persian Emperor Darius used a 2-kilometre (1.2 mi) pontoon bridge to cross the Bosphorus and Emperor Caligula built a 2-mile (3.2 km) bridge at Baiae in 37 AD.
For Emperor Darius I The Great of Persia (522–485 BC), the Greek Mandrocles of Samos once engineered a pontoon bridge that stretched across the Bosporus, linking Asia to Europe, so that Darius could pursue the fleeing Scythians as well as move his army into position in the Balkans to overwhelm Macedon.
Other spectacular pontoon bridges were Xerxes' Pontoon Bridges across the Hellespont by Xerxes I in 480 BC to transport his huge army into Europe:
and meanwhile other chief-constructors proceeded to make the bridges; and thus they made them: They put together fifty-oared galleys and triremes, three hundred and sixty to be under the bridge towards the Euxine Sea, and three hundred and fourteen to be under the other, the vessels lying in the direction of the stream of the Hellespont (though crosswise in respect to the Pontus), to support the tension of the ropes.
They placed them together thus, and let down very large anchors, those on the one side towards the Pontus because of the winds which blow from within outwards, and on the other side, towards the West and the Egean, because of the South-East and South Winds.
They left also an opening for a passage through, so that any who wished might be able to sail into the Pontus with small vessels, and also from the Pontus outwards.
Having thus done, they proceeded to stretch tight the ropes, straining them with wooden windlasses, not now appointing the two kinds of rope to be used apart from one another, but assigning to each bridge two ropes of white flax and four of the papyrus ropes.
The thickness and beauty of make was the same for both, but the flaxen ropes were heavier in proportion, and of this rope a cubit weighed one talent.
When the passage was bridged over, they sawed up logs of wood, and making them equal in length to the breadth of the bridge they laid them above the stretched ropes, and having set them thus in order they again fastened them above.
When this was done, they carried on brushwood, and having set the brushwood also in place, they carried on to it earth; and when they had stamped down the earth firmly, they built a barrier along on each side, so that the baggage-animals and horses might not be frightened by looking out over the sea.

According to John Hale's Lords of the Sea, to celebrate the onset of the Sicilian Expedition (415 - 413 B.C.), the Athenian general, Nicias, paid builders to engineer an extraordinary pontoon bridge composed of gilded and tapestried ships for a festival that drew Athenians and Ionians across the sea to the sanctuary of Apollo on Delos.
On the occasion when Nicias was a sponsor, young Athenians paraded across the boats, singing as they walked, to give the armada a spectacular farewell.

The late Roman writer Vegetius, in his work De Re Militari, wrote:
But the most commodious invention is that of the small boats hollowed out of one piece of timber and very light both by their make and the quality of the wood.
The army always has a number of these boats upon carriages, together with a sufficient quantity of planks and iron nails.
Thus with the help of cables to lash the boats together, a bridge is instantly constructed, which for the time has the solidity of a bridge of stone.

The emperor Caligula is said to have ridden a horse across a pontoon bridge stretching two miles between Baiae and Puteoli while wearing the armour of Alexander the Great to mock a soothsayer who had claimed he had "no more chance of becoming emperor than of riding a horse across the Bay of Baiae".
Caligula's construction of the bridge cost a massive sum of money and added to discontent with his rule.
The Greek writer Herodotus in his Histories, records several pontoon bridges. The Persian Emperor Darius used a 2-kilometre (1.2 mi) pontoon bridge to cross the Bosphorus and Emperor Caligula built a 2-mile (3.2 km) bridge at Baiae in 37 AD. For Emperor Darius I The Great of Persia (522–485 BC), the Greek Mandrocles of Samos once engineered a pontoon bridge that stretched across the Bosporus, linking Asia to Europe, so that Darius could pursue the fleeing Scythians as well as move his army into position in the Balkans to overwhelm Macedon. Other spectacular pontoon bridges were Xerxes' Pontoon Bridges across the Hellespont by Xerxes I in 480 BC to transport his huge army into Europe:
and meanwhile other chief-constructors proceeded to make the bridges; and thus they made them: They put together fifty-oared galleys and triremes, three hundred and sixty to be under the bridge towards the Euxine Sea, and three hundred and fourteen to be under the other, the vessels lying in the direction of the stream of the Hellespont (though crosswise in respect to the Pontus), to support the tension of the ropes. They placed them together thus, and let down very large anchors, those on the one side towards the Pontus because of the winds which blow from within outwards, and on the other side, towards the West and the Egean, because of the South-East and South Winds. They left also an opening for a passage through, so that any who wished might be able to sail into the Pontus with small vessels, and also from the Pontus outwards. Having thus done, they proceeded to stretch tight the ropes, straining them with wooden windlasses, not now appointing the two kinds of rope to be used apart from one another, but assigning to each bridge two ropes of white flax and four of the papyrus ropes. The thickness and beauty of make was the same for both, but the flaxen ropes were heavier in proportion, and of this rope a cubit weighed one talent. When the passage was bridged over, they sawed up logs of wood, and making them equal in length to the breadth of the bridge they laid them above the stretched ropes, and having set them thus in order they again fastened them above. When this was done, they carried on brushwood, and having set the brushwood also in place, they carried on to it earth; and when they had stamped down the earth firmly, they built a barrier along on each side, so that the baggage-animals and horses might not be frightened by looking out over the sea.
According to John Hale's Lords of the Sea, to celebrate the onset of the Sicilian Expedition (415 - 413 B.C.), the Athenian general, Nicias, paid builders to engineer an extraordinary pontoon bridge composed of gilded and tapestried ships for a festival that drew Athenians and Ionians across the sea to the sanctuary of Apollo on Delos. On the occasion when Nicias was a sponsor, young Athenians paraded across the boats, singing as they walked, to give the armada a spectacular farewell. 
The late Roman writer Vegetius, in his work De Re Militari, wrote:
But the most commodious invention is that of the small boats hollowed out of one piece of timber and very light both by their make and the quality of the wood. The army always has a number of these boats upon carriages, together with a sufficient quantity of planks and iron nails. Thus with the help of cables to lash the boats together, a bridge is instantly constructed, which for the time has the solidity of a bridge of stone.
The emperor Caligula is said to have ridden a horse across a pontoon bridge stretching two miles between Baiae and Puteoli while wearing the armour of Alexander the Great to mock a soothsayer who had claimed he had "no more chance of becoming emperor than of riding a horse across the Bay of Baiae". Caligula's construction of the bridge cost a massive sum of money and added to discontent with his rule.
Pontoon bridge