Following the Treaty of Fontainebleau signed between France and Spain in October 1807, which provided for the invasion and subsequent division of Portuguese territory into three kingdoms, French troops under the command of General Junot entered Portugal, which requested support from the British.
In July 1808 troops commanded by the Duke of Wellington, at the time known as Arthur Wellesley, landed in Portugal and defeated French troops at the Battles of  Roliça and Vimeiro.
This forced Junot to negotiate the Convention of Cintra, which led to the evacuation of the French army from Portugal.

However, the threat of further invasions by the French led Wellington, on October 20, 1809, to order the construction of defensive lines in order to protect Lisbon from Napoléon Bonaparte's troops and also to provide a route for his own evacuation should it be necessary.
Work on the Fort of Alqueidão, as part of the first Line of defence, began on November 8, 1809, at more or less the same time as improvements to the Fort of São Julião da Barra, close to Lisbon, and construction of the new Fort of São Vicente at Torres Vedras, under the overall supervision of Colonel Richard Fletcher who was commander of the Royal Engineers.
By October of the following year 126 forts, redoubts and other defences forming three lines of defence had been constructed over 80 kilometres, reinforcing the natural obstacles that the land offered and making maximum use of the existing topography.

A new French invasion was headed by Marechal  Masséna.
He was defeated in September 1810 by the Anglo-Portuguese army commanded by Wellington at the Battle of Buçaco.
 Despite this he forced the allies to retreat to the Lines of Torres Vedras, where a stalemate ensued for several months.
Masséna’s troops were gathered around Sobral de Monte Agraço but he found the line of defences, centered on the Fort of Alqueidão, to be impregnable.
He eventually had to retreat due to lack of food and supplies, withdrawing to the Spanish border.
However, works on the Lines continued after the French withdrawal, with 152 works eventually being completed.

The fort is at 439 meters above sea level, on top of the Monte Agraço mountain range, and occupies an area of 3.5 hectares.
It was part of a group of seven forts and redoubts in the 2nd section or district of the first of the Lines of Torres Vedras and designated No.
14 in the numbering system used for all of the works carried out on the lines.
Work on Alqueidão began on 4 November 1809.Wellington’s headquarters were close by in the village of Pêro Negro, and, because of its commanding position, the fort served as the command post for the Lines.
Using an optical telegraph signalling system, the fort could communicate with the Fort of Archeira to the south of Torres Vedras and from there to both the Fort of São Vicente to the north of the same town and the Atlantic coast.
 
The Fort of Alqueidão had a garrison of 1,590 men, and was equipped with 24 cannon, believed to be 14 12-pounder artillery, six 9-pouders, and four 6-pounders.
The troops were Portuguese, under the command of the British Brigadier-General Denis Pack, together with two artillery companies from Sobral formed and trained by William Beresford who was both a general in the British army and a marshal of the Portuguese army.
Following the Treaty of Fontainebleau signed between France and Spain in October 1807, which provided for the invasion and subsequent division of Portuguese territory into three kingdoms, French troops under the command of General Junot entered Portugal, which requested support from the British. In July 1808 troops commanded by the Duke of Wellington, at the time known as Arthur Wellesley, landed in Portugal and defeated French troops at the Battles of  Roliça and Vimeiro. This forced Junot to negotiate the Convention of Cintra, which led to the evacuation of the French army from Portugal.
However, the threat of further invasions by the French led Wellington, on October 20, 1809, to order the construction of defensive lines in order to protect Lisbon from Napoléon Bonaparte's troops and also to provide a route for his own evacuation should it be necessary. Work on the Fort of Alqueidão, as part of the first Line of defence, began on November 8, 1809, at more or less the same time as improvements to the Fort of São Julião da Barra, close to Lisbon, and construction of the new Fort of São Vicente at Torres Vedras, under the overall supervision of Colonel Richard Fletcher who was commander of the Royal Engineers. By October of the following year 126 forts, redoubts and other defences forming three lines of defence had been constructed over 80 kilometres, reinforcing the natural obstacles that the land offered and making maximum use of the existing topography.
A new French invasion was headed by Marechal  Masséna. He was defeated in September 1810 by the Anglo-Portuguese army commanded by Wellington at the Battle of Buçaco.  Despite this he forced the allies to retreat to the Lines of Torres Vedras, where a stalemate ensued for several months. Masséna’s troops were gathered around Sobral de Monte Agraço but he found the line of defences, centered on the Fort of Alqueidão, to be impregnable. He eventually had to retreat due to lack of food and supplies, withdrawing to the Spanish border. However, works on the Lines continued after the French withdrawal, with 152 works eventually being completed.
The fort is at 439 meters above sea level, on top of the Monte Agraço mountain range, and occupies an area of 3.5 hectares. It was part of a group of seven forts and redoubts in the 2nd section or district of the first of the Lines of Torres Vedras and designated No. 14 in the numbering system used for all of the works carried out on the lines. Work on Alqueidão began on 4 November 1809.Wellington’s headquarters were close by in the village of Pêro Negro, and, because of its commanding position, the fort served as the command post for the Lines. Using an optical telegraph signalling system, the fort could communicate with the Fort of Archeira to the south of Torres Vedras and from there to both the Fort of São Vicente to the north of the same town and the Atlantic coast.  
The Fort of Alqueidão had a garrison of 1,590 men, and was equipped with 24 cannon, believed to be 14 12-pounder artillery, six 9-pouders, and four 6-pounders. The troops were Portuguese, under the command of the British Brigadier-General Denis Pack, together with two artillery companies from Sobral formed and trained by William Beresford who was both a general in the British army and a marshal of the Portuguese army.
Fort of Alqueidão