The Lines of Torres Vedras were lines of forts built in secrecy to defend Lisbon during the Peninsular War. Named after the nearby town of Torres Vedras, they were ordered by Arthur Wellesley, Viscount Wellington, constructed by Sir Richard Fletcher, 1st Baronet, and his Portuguese workers between November 1809 and September 1810, and used to stop Masséna's 1810 offensive.
After his troubling Spanish experience at the Battle of Talavera, Wellington realised that, being outnumbered by the French forces, he might need to retreat to Portugal and possibly evacuate the peninsula, so decided to strengthen the proposed evacuation area around the fort at Oeiras e São Julião da Barra Portugal. He used a report of Colonel Vincent, ordered by Junot in 1807, describing the excellent defensive capacities in the region nearby Lisbon. Historian John Grehan suggested that the study by Major Neves Costa influenced Wellington's decision to construct the lines, but in fact the plans pre-dated Costa's study. He was also inspired by the Martello Towers along the English Channel coast. In October 1809 Wellington, after surveying the area personally with Lieutenant-Colonel Sir Richard Fletcher, ordered in his detailed memorandum dated 20 October 1809 the building of the Lines of Torres as a system of fortifications blockhouses, redoubts, ravelins, cuts of natural relief, etc. The work began on several of the main defensive works in November 1809.
When the results of Royal Engineer surveyors were gathered together, it was possible by February 1810 to begin works on 150 smaller interlinking defensive positions, using wherever possible the natural features of the landscape. The work received a boost after the loss to the French of the fortress at the Siege of Almeida (1810) in August, with the public conscription of Portuguese labourers. The works were sufficiently complete when the French troops arrived in October to make them stop and fall back. Even after the French had retreated from Portugal, construction of the lines continued, and in 1812 34,000 men were still working on them.
The work was supervised by Fletcher, assisted by Major John Thomas Jones, and 11 other British officers, four Portuguese Army engineers, and two KGL officers. The cost was around £100,000 (close upon £200,000 per the Corps of Royal Engineers), one of the least expensive but most remunerative military investments in history.
The country from Torres Vedras to Lisbon resembles nothing so much as a gigantic mountain-torrent instantaneously converted into solid earth. The ground flows down from north to south in great undulations, which now and again throw up abrupt peaks ending in a knob of bare rock, only to plunge down again into deep gullies and ravines; the character of the whole being rugged and inhospitable, and suggesting even at first sight innumerable facilities for a stubborn rear-guard fight.
Wellington's earliest idea had been to construct his first line from Alhandra on the east to Rio São Lourenço on the west, with advanced works at Torres Vedras, Monte de Agraço, and other commanding points. The tardiness of Masséna's movements, however, had enabled him to strengthen the first line sufficiently to warrant his holding it in permanence. Surveying this line from east to west, the first section from Alhandra almost to Arruda was about 5 miles (8.0 km) long, of which 1 mile (1.6 km), towards the river Tagus, had been inundated; more than another 1 mile (1.6 km) had been scarped into a precipice, and the most vulnerable point had been obstructed by a huge abatis. The additional defences included 23 redoubts mounting 96 guns, besides a flotilla of gunboats to guard the right flank on the Tagus; and this portion of the ground was occupied by Hill's division.
The second section extended from Arruda to the west of Monte Agraço, which last was crowned by a very large redoubt mounting twenty-five guns, with three smaller works to supplement it. Monte Agraço itself was held by Pack's brigade with Anglo-Portuguese 5th Division (Leith's) in reserve behind it, while the strong but less completely fortified country to eastward was entrusted to the British Light Division.
The third section stretched from the west of Monte Agraço for nearly eight miles to the gorge of the river Zizandre, a little to south of Torres Vedras. This was by nature very advantageous ground, but from want of time had been no further strengthened than by two redoubts which commanded the road from Sobral de Monte Agraço to Montachique. Here, therefore, were concentrated the 1st, 4th, and 6th divisions, under the eye of Wellington himself, who had established his headquarters at Pêro Negro.
The last and most westerly section of the first line ran from the gorge of the Zizandre to the sea, a distance of nearly 12 miles (19 km), more than half of which, however, on the western side had been rendered impassable by the damming of the Zizandre and by the conversion of its lower reaches into one huge inundation. The chief defence consisted of the entrenched camp of Sao Vincente, a little to the north of Torres Vedras, which dominated the paved road leading from Leiria to Lisbon; and the force assigned to this portion of the ground was Picton's division.
The second line of defence was still more formidable, but, since the enemy was never able to force the first line, it must suffice to say that along all three of its sections from Quintella on the Tagus to Bucellas, from Bucellas to Mafra, and from Mafra to the sea a total distance of 22 miles (35 km) the British engineers had lavished every resource of construction and destruction to close all possible points of access to the French.
Lastly, in the event of failure even in the face of all these precautions, very powerful lines, 2 miles (3.2 km) long, had been thrown up round Oeiras e São Julião da Barra to cover an embarkation if it became necessary.
The lines were divided up into districts by Wellington in letter dated 6 October 1810:
Each district was allocated one Captain and one Lieutenant of Engineers.
The total number of troops to Wellington's hand for the defence of the entire position amounted, exclusive of two battalions of marines in the lines round São Julião, to 42,000 British, of whom 35,000 were effective; in addition to which he had over 27,000 Portuguese regulars, of whom 24,000 were effective; about 12,000 Portuguese militia; and 20–30,000 of the ordenanças, which last were of little value except for guerilla warfare. Lastly, the Marquis of la Romana with great generosity brought 8,000 Spaniards of his division likewise within the lines about Mafra. Altogether, therefore, Wellington had some 60,000 regular troops whom he could depend upon, and 20,000 more who could be trusted at least to fight behind earthworks.
The redoubts of the first line did not require more than 20,000 men to defend them, which left the whole of the true field-army free not only to reinforce any threatened point but also to make a counter-attack. To facilitate such movements a chain of signal-stations had been formed from end to end of the lines, and lateral roads of communication had been made so as to enable the troops to pass rapidly along their entire length.
Wellington did not abuse his fortified position by distributing his troops, according to the vicious cordon-system, in small fractions along the entire front, but kept his field-army for the most part in two masses on the centre and right, so that the whole could be assembled in a few hours.
The efficiency and cohesion of the lines was based on five points:
1) Redoubts of artillery with Portuguese artillerymen, commanded by Major-General José António Rosa, and situated to fire into preset zones, where the enemy attack was expected. Both lines extended more than 80 km. The first line had 534 artillery pieces.
2) Military roads to cover the rear of the lines and allowing an extraordinary mobility of forces. It allowed for the supply of combat supplies (ammunition, rations and water) to be provided by the Royal Waggon Train. In September 1810, the field army had some 66,598 regular soldiers. Including the Ordenanças and Milicias, it had 77,690 men.
4) Secrecy. The building of the lines took, surprisingly, only 10 to 11 months. Everything was preserved as a secret, the maintenance of which was as surprising as the lines' construction. Only one report appeared in the London newspapers, a major source of information for Napoleon. It is said that when Masséna was first confronted by the Lines, he asked his staff why they had not known about them in advance. When he was told "Wellington has made them", Masséna shouted "The devil [he did], Wellington didn't make the mountains!" It is also said that not even the British government knew about the forts and was stunned when Wellington first said in despatches that he had retreated to them.
5) The scorched earth policy. North of the lines everything that could supply the invading army was collected, hidden or burnt. A vast tract of land was deserted and perhaps 200,000 inhabitants of the neighbouring districts of the lines were relocated inside the lines. That the French were able to campaign in their vicinity at all was a remarkable feat, according to Wellington:
It is certainly astonishing that the enemy have been able to remain in this country so long; and it is an extraordinary instance of what a French army can do. ...They brought no provisions with them, and they have not received even a letter since they entered Portugal. With all our money, and having in our favour the good inclinations of the country, I assure you that I could not maintain one division in the district in which they have maintained not less than 60,000 men...for more than two months.
The Anglo-Portuguese Army was forced to retreat to the lines after winning the Battle of Buçaco (27 September 1810). The French army under Marshal André Masséna discovered a barren land (under the scorched earth policy) and an enemy behind an impenetrable defensive position. Masséna's forces arrived at the lines on 11 October and took Sobral de Monte Agraço the following day. After driving in the Anglo-Portuguese skirmish line on 13 October, the VIII Corps tried to push forward on the 14th. In the Battle of Sobral they were repelled in an attempt to assault a strong British outpost.
After attempting to wait out the enemy, the lack of food and fodder, in the area north of the Lines, meant that Masséna was forced to order a French retreat northwards, starting on the night of 14/15 November 1810, to find an area that had not been subjected to the scorched earth policy.
In December, fearing a French attempt on the left of the Tagus a chain of redoubts were constructed, 17 in number, from Almada to Trafaria. The French however made no movement, and still holding out, through February when starvation really set in, Marshal Masséna ordered, at the beginning of March 1811, a retreat, that took a month, to get to Spain.
Marshal Masséna began his campaign with his army (l'Armée de Portugal) at 65,000 strong. Losing 4,000 at the Battle of Buçaco he arrived at Torres Vedras with 61,000 men. When he eventually reached Spain, in April 1811, he had lost a further 21,000 men. One of the coldest winters the area had ever seen hit Portugal and killed many of the French forces. They had also been hit by starvation, severe illness and disease, killing the soldiers in their thousands. The human cost was also great for the local population, because of the privations they endured. It is estimated that between October 1810 and March 1811 about 50,000 Portuguese died of hunger or disease.
The Allies were reinforced by fresh British troops in 1811 and renewed their offensive. They left the lines, following the French retreat. The lines were not needed again for the rest of the Peninsular War.
The military history John Fortescue stated in 1896 that it was too often assumed that the success of the lines of Torres Vedras was due to mere skilful use of the spade. Colonel Fletcher, who was entrusted with the execution of Wellington's broad designs, deserves, together with his subordinates of the engineers, all credit for his ingenuity and thoroughness; but, given time, labour, and favourable ground, it does not need a great general to construct a formidable line of entrenchments. On the other hand, it does require a great general so to use such a line that it shall always be a source of strength and not of weakness. Villars at La Bassée flattered himself to his cost that his Lines of Ne Plus Ultra (Latin for "no further") would stop Marlborough during the campaigning season of 1711. They did not. To check great leaders such as Marlborough and Masséna there must be not only lines but a man.
Substantial portions of the lines survive today, albeit in a heavily decayed condition due to locals re-using 100,000 tons of stones. Some conservation and restoration work has been undertaken in recent years using European Community funding. This work was awarded the European Union Prize for Cultural Heritage / Europa Nostra Award for this conservation work in 2014.