The Lines of Torres Vedras, on the peninsula north of Lisbon, are the most famous fortifications of the Napoleonic Wars, and in 1810 were the only thing that saved Wellington from having to evacuate his army from Portugal during Marshal Masséna’s invasion of the country. When the British government was deciding whether to return to Portugal after the evacuation from Corunna, Wellington had declared that he could defend the country against any army smaller than 100,000 strong, and that the French could not spare that many men for the invasion of Portugal. Despite this confidence, on his return to Portugal in April 1809 Wellington had noted the defensive potential of the Lisbon peninsula,
The idea of defending Lisbon against the French on the hills to the north had been in the air since 1808. The credit can be split between Major Jose Maria das Neves Costa of the Portuguese army, and Wellington himself. Towards the end of 1808 Costa carried out a detailed survey of the hills, and in the spring of 1809 submitted his ideas to the Portuguese regency.
Wellington had also examined the ground north of Lisbon, during the negotiations that led to the signing of the Convention of Cintra, and had recognised how easily they could be defended. In October 1809 he returned to the area with his chief engineer, Colonel Sir Richard Fletcher, and on 20 October, after examining the ground, issued the Memorandum that officially marked the start of work on the Lines of Torres Vedras.
Lisbon lies at the southern end of a peninsular formed by the Atlantic to the west and the Tagus to the east. Further north the terrain is mountainous, but the area south of Torres Vedras, where the defences were built, is hilly, reaching a high point of just over 410m (1,350ft) south of Sobral.
On a detailed map the hills north of Lisbon look to be a complex mess, but in fact the general topography of the area is quite straightforward. The highest ground is on the western side of the peninsula, reaching close to the Tagus around Alverca. From that point two lines of higher ground stretch out towards the Atlantic, one running north west towards Sobral and one running west, past Bucellas and towards Mafra. This second line is the stronger of the two, with higher ground most of the way to the Atlantic, and the gap filled by the valley of the River San Lourenco.
The first line (to Sobral) is longer, and its western half is much lower lying. The valley of the River Zizandre reaches as far as Sobral, but to reach this area the French would have had to march around the Serra de Monte Junta, which stretches fifteen miles north of the Zizandre without being crossed by a single good road. The eastern part of the valley was defended by strong fortifications based around Torres Vedras, while the western part was carefully flooded, creating an impassable bog.
When work first began on the defences of Lisbon, the plan was to build two full lines, one close to Lisbon to act as a point of final refuge, and the second across the peninsula from Alverca, through Mafra, reaching the Atlantic along the River San Lourenco. Further north the line from Alverca to Sobral, and then on to Torres Vedras was seen as a line of outposts, to be held for as long as possible and then abandoned, with its defenders falling back to the main line. When work began on the lines, Wellington expected the French to turn against him at any moment, but instead they invaded Andalusia, and Wellington’s engineers gained an extra year to build their defences. By the time Wellington finally retreated back into the lines, the first line was so strong that Wellington decided to make it his main line of defence.
Despite their name, the Lines of Torres Vedras were actually made up of a series of separate fortifications, carefully placed to provide each other with covering fire. These forts varied in size from the massive fort at Torres Vedras, designed to hold 5,000 men, down to small gun emplacements designed to mount three guns and 200 men.
In theory each of these forts had to meet a series of minimum requirements. The ditch was to be 15ft wide at the top and at least 10ft deep, and the top of the parapet should be at least 5ft higher than the top of the counterscarp (the far wall of the ditch). The parapets themselves were never more than 10ft wide, with some only 2ft wide. Each fort could be protected by fire from its neighbours.
Hundreds of tons of earth were moved in front of line lines. Some of this work was done to remove blind spots, where the French could have hidden from gunfire from the forts, while in other areas the hills were cut away to create virtual cliff faces that the French would have to climb before they could reach the forts (one of the longest stretches saw a 2000 yard long cliff created near ALhandra). Sunken roads were filled up and houses demolished to deny the French any cover. In some areas valleys ran through the lines, and these were filled with an abattis made up of entangled olive trees. These were very difficult to remove, impossible to actually move through, but did not block grapeshot.
The defensive work continued north of the lines themselves. Wellington’s engineers made preparations to destroy every road and bridge that the French might use to approach the fortifications.
The western end of the first line was defended by building dams to block the River Ziznadre. These created a flooded area several miles long, surrounded by bogs. The dams themselves were protected by forts that were out of range of any guns in the French field army.
The Lines of Torres Vedras were designed by Wellington’s Chief Engineer, Colonel Sir Richard Fletcher. Wellington’s army was always desperately short of trained engineers. Fletcher was supported by 11 British, four Portuguese and two German engineering officers and eighteen rank and file from the engineers. A further 150 men were detached from the main army to help.
The work itself was carried out the Portuguese. The Lisbon militia served for an extra 4d per day. Between 5,000 and 7,000 paid labourers were employed at between 1s and 1s. 8d. per day (in comparison a British solder was paid 1s.). Finally the declaration of a state of emergency by the Portuguese regency allowed Fletcher to conscript thousands of peasants from the local area, although they were paid at the same rate as the labourers. Each engineering officer commanded a gang of 1,000-1,500 men. In effect Fletcher and his men had access to unlimited labour.
One of the most impressive features of the construction of the Lines of Torres Vedras was that their existence was kept almost completely secret from the French, and even to a certain extent from the British and Portuguese armies. Even some of Fletcher’s engineers are said not to have realised exactly what they had built. The French first discovered that there were some fortifications around Lisbon while marching south from Coimbra, on what they had believed was the final stage of their victorious campaign. It was only when they actually reached the lines on 11 October 1810 that the French realised that they were facing something out of the ordinary.
One key feature of Wellington’s plan was that his field army would not provide the garrison of the forts. Instead his divisions would retreat through the lines, and then take up their positions behind the forts. If the French did make a serious attack on any part of the lines, then Wellington would concentrate his army against it, and any French column that did manage to fight its way through a gap in the lines would be crushed.
The forts themselves were to be manned by the Portuguese militia, 8,200 infantry and 2,800 artillerymen. They were supported by 250 British artillerymen, 2,000 marines from the British ships off Lisbon and 4,000 Portuguese line infantry who had never joined the main army. When the French eventually reached the lines, Wellington’s field army provided an outlying line of pickets, and the only fighting would involved the outlying troops at Sobral.
By the time Masséna reached the Lines of Torres Vedras he was actually outnumbered. Wellington had 35,000 British troops, 24,500 Portuguese troops and 8,000 Spanish troops under arms, giving him a field army of 67,500 men, supported by the 12,400 militia in the line and an unknown number of Ordenança. Masséna had just over 50,000 men left in the Army of Portugal.
The Lines of Torres Vedras cost £100,000 to build. At a time when an infantryman was paid 1s per day, the lines cost the equivalent of paying 5,500 infantrymen (less than one full division) for one year. When the French arrived in front of the lines they were so intimidated by what they saw that they never actually launched a full scale attack on the lines. After two skirmishes at Sobral (first combat of Sobral, 12 October 1810 and second combat of Sobral, 14 October 1810), the French settled down to conduct a pointless siege of the lines, before after a month pulling back to Santeram. In fact the Lines of Torres Vedras could be said to have been too strong, for Wellington had hoped that the French would at least to attempt to fight their way through, giving him a chance to inflict a heavy defeat on Masséna.
The retreat into the Lines of Torres Vedras had a tragic aftermath. Around 300,000 people were forced to abandon their homes and retreat behind the lines, and over the winter of 1810-11 40,000 people are said to have died around Lisbon. Wellington had underestimated the French ability to forage, even in apparently desolate countryside. He had expected the French to be forced to retreat out of Portugal within a few days of reaching the Lines, but instead Masséna managed to hold on at Santeram until March 1811.
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