Lines of Torres Vedras (1810): Wellington's Secret Defences

The Lines of Torres Vedras were a chain of forts and earthworks built across the peninsula north of Lisbon in 1809–1810 to protect the Portuguese capital from French invasion. Planned by Arthur Wellesley, Viscount Wellington, and built largely by Portuguese labour, they stopped Marshal Masséna’s army in October 1810 without a major battle. Starved and sickened in front of the lines, the French were forced to retreat from Portugal in 1811, a turning point in the Peninsular War.

Background

After the Dos de Mayo uprising and the start of the war in Spain, Britain sent an army to Portugal, its oldest ally. By 1809 Wellington commanded the British forces and had driven the French out of northern Portugal, but he knew Napoleon could send far larger armies once the war with Austria was over.

Wellington’s strategy was to keep a secure base around Lisbon, the port through which his supplies came and from which his army could be evacuated if necessary. On 20 October 1809 he issued a memorandum to his chief engineer, Lieutenant-Colonel Richard Fletcher, setting out the main lines of defence.

Building the lines

Construction began in late 1809 and continued through 1810. British engineer officers supervised thousands of Portuguese workers, including civilian labourers and militiamen, who were paid for their work. Rather than one continuous wall, the engineers built a network of mutually supporting redoubts on hilltops, linked by obstacles: river valleys were dammed and flooded, slopes were cut into steep scarps, roads were blocked, and trees and vines were cleared to open fields of fire.

There were three main lines. The first ran about 46 kilometres (29 miles) from Alhandra on the Tagus estuary to the mouth of the Sizandro river on the Atlantic, passing the town of Torres Vedras. The second, about 39 kilometres (24 miles) long and the strongest, lay several miles further south. A third, much shorter line surrounded São Julião da Barra at the mouth of the Tagus to cover an evacuation by sea.

By the time the French arrived, the system had more than 120 forts and redoubts and several hundred guns (works added later brought the total to around 150), manned mainly by Portuguese militia and gunners and by British marines and artillery. A chain of signal stations, adapted from naval signalling, allowed messages to pass along the lines in minutes.

Behind the lines, Wellington’s field army of British and Portuguese troops was positioned to move quickly to any threatened point, using roads built specially for the purpose. Royal Navy gunboats on the Tagus covered the eastern end, while the Atlantic coast protected the west. The system was therefore not a passive wall but a fortified zone in which a mobile army could fight on ground of its own choosing.

The scorched-earth policy

Wellington combined the lines with a deliberate policy of denying food to the enemy. The Portuguese government ordered people living between the frontier and the lines to leave their homes and to take or destroy crops, mills and livestock. The policy caused great suffering among Portuguese civilians, many of whom died of hunger and disease as refugees, but it left the French with almost nothing to eat.

Masséna’s invasion

In 1810 Napoleon sent Marshal André Masséna into Portugal with around 65,000 men. Wellington fell back, fighting a defensive action at Bussaco on 27 September 1810, and ordered the population to abandon the countryside in the French path and destroy or remove food. Thousands of refugees crowded into Lisbon.

Masséna reached the lines on 11 October 1810 and was reportedly astonished by their strength. After probing attacks around Sobral in mid-October, he decided an assault would fail. His army waited in front of the lines for about a month in a stripped countryside, then withdrew in mid-November to Santarém. In March 1811 the French began a full retreat from Portugal, harassed by Wellington’s army. Masséna lost about 25,000 men during the campaign, the great majority to hunger, disease and capture rather than battle.

Key people

• Wellington (1769–1852) – British commander in the Peninsula, who conceived the defensive plan.
• Richard Fletcher (1768–1813) – Royal Engineer officer who directed the construction; he was killed at the siege of San Sebastián in 1813.
• André Masséna (1758–1817) – one of Napoleon’s ablest marshals, whose invasion foundered before the lines.

Legacy

The lines were never seriously attacked, which is exactly why they mattered: they won a campaign by defence and starvation rather than battle. Portugal was never again invaded by the French, and from this secure base Wellington went on to advance into Spain from 1812, contributing to Napoleon’s eventual defeat that ended at Waterloo.

Many of the forts survive, and several, including the Fort of São Vicente at Torres Vedras, were restored for the bicentenary in 2010 and can be visited along a historic route.

Timeline

• 1809, 20 October: Wellington’s memorandum orders the building of the lines.
• 1809, November: Construction begins under Richard Fletcher.
• 1810, 27 September: Battle of Bussaco.
• 1810, 11 October: Masséna’s army arrives in front of the lines.
• 1810, 14 November: French begin to fall back towards Santarém.
• 1811, 5 March: Masséna starts his retreat from Portugal.

Why it matters

The Lines of Torres Vedras saved Lisbon and Portugal, preserved Wellington’s army and showed how fortification, planning and scorched-earth tactics could defeat a stronger enemy. They are among the most remarkable military engineering projects of the Napoleonic Wars.