#appian

Hey, thanks for the question.

He technically didn't fell off the bridge, the bridge collapsed but weeeel.

It happened during the Illyrian campaign (35-33 BCE), so he's not 'Augustus' yet.

It's basically that short instance described in Suetonius 'Live of the Ceasars' :

"He carried on but two foreign wars in person: in Dalmatia, when he was but a youth, and with the Cantabrians after the overthrow of Antony. He was wounded, too, in the former campaign, being struck on the right knee with a stone in one battle, and in another having a leg and both arms severely injured by the collapse of a bridge. " (Suet. Div. Aug. 20.1)

and a bit more detailed in in App. Ill. IV 20:

"Some of the barbarians ran from the parapet to meet the Romans who were crossing, while others, unseen, sought to undermine the bridges with their long spears. They were much encouraged at seeing one bridge fall and a second one follow on top of it. When a third one went down a regular panic overtook the Romans, so that no one ventured on the fourth bridge until Augustus leaped down from the tower and reproached them. As they were not roused to their duty by his words, he seized a shield and sprang upon the bridge himself. Agrippa and Hiero, two of the generals, and one of his bodyguard, Lucius, and Volas ran with him, only these four with a few armor-bearers. He had almost crossed the bridge when the soldiers, overcome by shame, rushed after him in crowds. Then this bridge, being overweighted, fell also, and the men on it went down in a heap. Some were killed and others were carried away with broken bones. Augustus was injured in the right leg and in both arms. Nevertheless, he ascended the tower with his signals forthwith and showed himself safe and sound, lest dismay should arise from a report of his death. In order that the enemy might not fancy that he was going to give in and retire he began to construct new bridges; by which means he struck terror into the Metulians, who thought that they were contending against an unconquerable will.

Joseph Lusher as Enobarbus (left) and Nick Baldasare as Mark Antony (right) from Shakespeare’s Antony & Cleopatra, Actors Theatre Columbus 1997

"Antonius sailed from Corcyra into the Adriatic with only a small number of troops, but with 200 ships which he had built in Asia. He discovered that Ahenobarbus was coming to meet him with his ships and a strong military force. Some believed that Ahenobarbus might not observe the terms of the agreement that had been exchanged between them (for not merely was he one of the men who had been condemned for the murder of Caesar, but after his condemnation he had also been proscribed and had fought against Antonius and Octavian at Philippi), but Antonius none the less sailed on with five of his best ships, to show his trust, and ordered the rest to follow at a distance. When Ahenobarbus came in sight with his whole fleet and all his troops, rowing towards them at full speed, Plancus, who was standing beside Antonius, was frightened and asked him to take way off the ship and send someone ahead to investigate this ambiguous behaviour. Antonius replied that he would rather die as a result of a breach of treaty than be recognized as a coward and live, and sailed on. They were now close to each other, and the flagships were identifiable from their ensigns and rowing towards each other. Then Antonius' chief lictor, standing in the bows, as is the custom, and either forgetting that the man who was approaching was of ambiguous loyalty and also commanded troops of his own, or else acting from a somewhat aristocratic attitude of mind, as though subjects or inferiors were coming to meet him, ordered them to lower their ensign. They did so and turned their ship to bring it alongside Antonius'. When the principals caught sight of each other they exchanged greetings, and Ahenobarbus' army saluted Antonius as Imperator. Plancus managed to recover his nerve, and Antonius received Ahenobarbus on board his own ship. They then sailed to Paloeis, where Ahenobarbus had his infantry, and there Ahenobarbus gave up his own tent to Antonius."

(Appian, The Civil Wars, Book V, §8)