Loison had entrusted the details of the attack on the bridge to Delaborde, whose infantry held the advanced posts. That officer first tried to approach the head of the bridge by means of a flying sap; but when it had advanced a certain distance the fire of the Portuguese from across the river became so deadly, that after many men had been killed in the endeavour to work up to the palisades on the bridge, the attempt had to be abandoned. The next device recommended by the engineers was that an attempt should be made to lay a trestle bridge at a spot some way below the town, where a mill-dam contracted the width of the angry river. This was found to be impossible, the stream proving to be far deeper than had been supposed, while the Portuguese from the left bank picked off many of the workmen [April 25].
Soult was now growing vexed at the delay, and sent two guns of position from Oporto to Loison, to enable him to subdue the fire of the enemy’s batteries. He also offered to call up Heudelet’s division from Braga, even at the cost of abandoning his hold on the northern part of the province of Entre-Douro-e-Minho. But a mere increase of his already considerable force would have been of no service to Loison; it was a device for passing the Tamega that he needed.
Such a scheme was at last laid before him by Captain Bouchard, one of his engineers[318]. The French officers had discovered, by a careful use of their glasses, that the Portuguese mine, which was to destroy the bridge, was situated in its left-hand arch, and that the mechanism by which it was to be worked was not a ‘sausage’ or a train of powder[319], but a loaded musket, whose muzzle was placed in the mine, while to its trigger was attached a cord which ran to the nearest trenches beyond the river. The musket was concealed in a box, but its cord was visible to those provided with a good telescope. Bouchard argued that if the cord could be cut or broken, the enemy would not be able to touch off the mine, and he had thought out a plan for securing his end. He maintained that an explosion at the French side of the bridge would probably sever the cord without firing the mine, and that a sudden assault, made immediately after the explosion, and before the Portuguese could recover themselves, might carry the barricades. In spite of the strongly-expressed doubts of Foy and several other generals, Bouchard was finally permitted to carry out his scheme.
He executed it on the night of May 2, when a dense fog chanced to favour his daring and hazardous proceedings. Having first told off some tirailleurs to keep up a smart fire on the enemy’s trenches and distract his attention, he sent four sappers, each provided with a small powder-barrel, on to the bridge. The men, dressed in their grey capotes, crawled on hands and knees, each rolling his barrel (which was wrapped in cloth to deaden the sound) before him. They kept in the shadow, and getting close under the parapet of the bridge crept on till they reached the outermost Portuguese palisade. One after another, at long intervals, each got forward unobserved, left his barrel behind, and crawled back. The fourth sapper, starting to his feet on his return journey, was observed by the Portuguese and shot down, but Silveira’s men did not realize what he had been doing, and merely took him for some daring explorer who was endeavouring to spy out the state of the defences. After waiting for an hour, Bouchard sent out a fifth sapper, who dragged behind him a ‘sausage’ of powder thirty yards long, which he successfully connected with the four barrels. All was now ready, and a battalion of picked grenadiers from Delaborde’s division, filed silently down into the street near the bridge-head: a whole brigade came behind them.
At two o’clock Bouchard fired his sausage, and the explosion followed. There were two chances of failure—one that the apparatus for firing the mine might not be disturbed by the concussion, the other that the shock might prove too strong, reach the mine, and destroy the bridge. Neither of these fatalities took place: the explosion duly broke the cord, shattered the nearest palisades, but did not affect the mine. Before the smoke had cleared away Delaborde’s grenadiers had dashed out on to the bridge, scrambled over the barricades, and driven off the guard on the further side. Regiment after regiment followed them, and charged up the mountain-side towards Silveira’s batteries and entrenchments. None of the Portuguese were under arms, save the few companies guarding the debouches from the bridge. These were swept away, and the French columns came storming into the bivouacs of the enemy before he was well awake. Hardly half a dozen cannon shots were fired on them from the batteries, and the greater part of the army of the Tras-os-Montes fled without firing a shot. Silveira escaped almost naked by the back window of the house above the bridge in which he had been sleeping.
All the ten guns in the Portuguese batteries, five standards, and several hundred prisoners fell into the hands of the victorious French, who lost (it is said) no more than two killed and seven wounded. Their good fortune had been extraordinary: without the opportune fog which hid their advance, their preliminary operations would probably have been discovered. If their explosion had done a little more or a little less than was hoped, the bridge might have been totally destroyed, or its barricades left practically uninjured—either of which chances would have foiled Bouchard’s plan. But the luck of the army of Portugal was still in the ascendant, and all went exactly as had been intended.
Thus the Tamega was passed, and Silveira decisively beaten: his levies had fled in all directions, and Soult opined that it would take a long time to rally them. The day after the fight Loison was joined at Amarante by Heudelet’s division from Braga, which, in obedience to the Marshal’s orders, had marched to join the expeditionary force, leaving only a single battalion behind to hold Viana. This was an unfortunate move, as on Heudelet’s departure the Ordenanza came down from the Serra de Santa Catalina, and overran the district which had been evacuated, in spite of Lorges’ dragoons, who had been directed to keep the roads clear after the infantry had been withdrawn.
Meanwhile there were far more troops at Amarante than were needed for the pursuit of Silveira, so Soult called back to Oporto the division of Delaborde, leaving to Loison the infantry of Heudelet and Sarrut, with Lahoussaye’s two brigades of dragoons, a force of about 7,000 men. He ordered his lieutenant to scour the country as far as Villa Real, and to send reconnaissances on the roads toward Chaves and Braganza, with the object of frightening the insurgents to retreat as far as possible. But Loison was not to advance for more than two days’ march into the Tras-os-Montes, for rumours were beginning to arrive concerning the appearance of British troops in the direction of Coimbra, and the Marshal wished to keep his various divisions close enough to each other to enable them to concentrate with ease. If there were any truth in the news from the south, it would be dangerous to allow a force which formed a third of the whole army of Portugal to go astray in the heart of the mountains beyond the Tamega. Loison accordingly marched off on May 8 towards Villa Real, which he occupied without meeting with resistance. He learnt that Silveira and his regulars had crossed the Douro, and gone off in the direction of Lamego; but Botilho had fled up the Tamega towards Chaves, and the Ordenanza were lurking in the hills. He then returned to Amarante, where we may leave him, at the end of his tether, while we describe the state of affairs in Oporto.