"In 1809 French armies controlled almost every province of Spain and only Wellington’s small force in Portugal stood between Napoleon and the conquest of Iberia.
The French invaded Portugal in the summer of 1810 but found their way blocked by the most extensive field fortifications the world had ever seen – the Lines of Torres Vedras. Unable to penetrate the Lines, the French were driven back into Spain having suffered the heaviest defeat yet experienced by Napoleon’s armies. The retreat from Portugal marked the turning point in the Peninsular War and, from the security of the Lines, Wellington was able to mount the offensive campaigns that swept France’s Imperial armies back across the Pyrenees.
The Lines of Torres Vedras is an authoritative account of the planning, construction and occupation of the Lines and of the battles, sieges and horrors of the French invasion. It is also an important study of Wellington’s strategy during the crucial years of the war against Napoleon.
‘This is a well-researched, well-written, closely argued and fascinating contribution to the historiography of the Peninsular War.’ The Spectator
‘Essential reading for every Peninsula enthusiast, this is recommended highly.’ Military Illustrated"
Perhaps you could compare/contrast the two books?
I prefer: WELLINGTON AND THE LINES OF TORRES VEDRAS The Defence of Lisbon during the Peninsular War, 1807-1814 In October 1810, the Third French invasion of Portugal under Maréchal Masséna arrived at the Lines of Torres Vedras and his triumphal march into Lisbon came to an abrupt halt. Five months later a thoroughly demoralised and defeated French army retreated from Portugal and never returned. The Lines played a vital role in enabling the allied army to operate against a more numerous enemy. When threatened, there was a safe place for the allies to retire to, and from this secure base, Wellington eventually liberated the Iberian Peninsula. France, Portugal and Britain developed plans for the defence of Lisbon in 1808 and 1809. In November 1809, the British proposal was commenced and became the Lines of Torres Vedras. The Memorandum on the construction was written in October 1809 but was more of an outline. The design and construction was completed over the next 18 months, the bulk being completed before the arrival of the French in October 1810. The initial design was expanded through 1810 as more time became available and the construction in October 1810 was significantly different to the original memorandum. The book takes the reader through events in 1809 that led to the need for the construction of defences. The construction work is detailed and illustrated through several maps to explain the position and purpose of the several defences. The French invasion of 1810 is summarised through to the time when the French arrived at the Lines. The operations and movements over the next month are again detailed along with the continuing construction work on the Lines. One of the unusual elements of the defences was the construction of a telegraph system and this is described in great detail. One of the lesser-known facts about the Lines, is the position of the opposing forces between October 1810 and March 1811. They were only facing each other at the Lines for a few weeks during this period and most French troops never approached them. The operations and defences were spread over a much larger area. This book uses many new sources to prove a new, in-depth, English language account of the massive engineering exercise that built the Lines with the help of thousands of Portuguese civilians. Without the construction of the Lines, it is likely that Portugal would have been lost and history would tell a very different story. https://www.helion.co.uk/military-history-books/wellington-and-the-lines-of-torres-vedras-the-defence-of-lisbon-during-the-peninsular-war-1807-1814.php