Moore's assessment of Portugal was not entirely invalid and Wellington agreed with him that 'the whole country is frontier, and it would be difficult to prevent the enemy from penetrating by some point or other. [4]

The Serra da Estrella, the mountain range which divides the Beira frontier.

Portugal's border with Spain runs for some 900 miles but there were few really practical invasion routes in 1810 for a large army and its vast train. Portugal's main centres of population, wealth, commerce and education were all (and still are) to be found along its coastal strip. The land round the frontier was sparsely populated. Large areas were mountainous, inhospitable and uncultivated.

Wellington therefore, from both a military and a moral perspective, saw little point in trying to defend such an area. '(T)he line of frontier of Portugal is so long in proportion to the extent and means of the country, and the Tagus and the mountains separate each other, and it is open in many parts, that it would be impossible for an army, acting upon the defensive, to carry on its operations upon the frontier without being cut off from the capital.' Wellington, consequently, had no intention of trying to stop the invader on the border. 'The scene of the operations of the army would, therefore most probably be considerably within the frontier, whether their attack be made in winter or summer. [5]

The object of the defending forces, Wellington told his Chief Engineer, 'should be to oblige the enemy as much as possible to make his attack with concentrated corps. They should stand in every position which the country could afford such a length of time as would enable the people of the country to evacuate towns and villages, carrying with them or destroying all articles of provisions and carriages. [6]

Wellington then intended to 'bring matters to extremities, and to contend for the possession and independence of Portugal in one of the strong positions in this part of the country. [7]

He could not risk engaging a superior French force with the small army under his command, however, unless he was able to fortify his defensive positions in advance. It was upon these fortifications that the whole of Wellington's defensive policy was founded.

For Wellington's plan to work it was obviously essential for him to calculate accurately the precise route that the invaders would take. The Portuguese frontier with Spain is naturally divided into three definable sections. The northernmost, that from the mouth of the River Minho to the River Douro, was not within the scope of French operations in 1810.

It can only be reached from Galicia and the French had not at that time subdued this province nor had they any intention of dealing with it until after the conquest of Portugal. The occupation of this northern area of Portugal, or even its regional capital, Oporto, would not have brought about any significant result. Lisbon, unlike its counterpart, Madrid was not only the political but also the moral and economic heart of the country and whilst it remained free, Portugal remained unconquered. To reach Lisbon from the north two major rivers have to be crossed, the Douro and the Mondego. It would have been virtually impossible for the invading army to force the passage of either of these obstacles in the face of a hostile enemy.

The other two sections of the Portuguese frontier, from the Douro to the Tagus, and from the Tagus to the Guadiana, were both accessible to the French in 1810. This was because they were in possession of the plains of Leon and La Mancha, and of northern Andalucia. However, only the roads that ran north of the Tagus travelled directly to the gates of Lisbon. Any advance south of that river would only lead the invader to the height of Almada, where he would still be separated from the capital by the estuary of the Tagus.

As the Royal Navy maintained a strong presence in the Lisbon basin, a French army camped at Almada would still be as far from success as when it had started out from Spain. For a further thirty miles upstream from Lisbon, the Tagus remained an impassable barrier for an army of the nineteenth century.

From the capital northwards almost as far as Alhandra, the Tagus forms a broad lagoon, in parts eleven miles wide. Beyond Alhandra. the river contracts to a normal breadth, but for another ten miles upstream the eastern bank of the river is bordered with saltmarshes and broken by rivulets. It is only near Salvaterra de Magos that the river could be bridged.

An invader from Spanish Extramadura. could cross it here or at any point upstream, but the nearest permanent bridge at that time was another sixty miles north at Abrantes. It was therefore extremely unlikely that the principal French effort would be delivered south of the Tagus. If used in conjunction with an attack from the north, however, an approach from the south might prove highly dangerous. 'The enemy will probably attack on two distinct lines, the one south, the other north of the Tagus,' Wellington told Colonel Fletcher, 'and the system of defence must be founded upon this general basis ... His object will be, by means of the corps north of that river, to cut off from Lisbon the corps opposed to him, and to destroy it by an attack in front and rear'. [8]

This was Wellington's greatest fear. A threat from the Northern frontier could draw the Anglo-Portuguese army away from the Lisbon peninsula. This could allow a subsidiary force from the south to bridge the Tagus and cut Wellington's army off from the capital. Wellington decided that if the French had a field army anywhere in the vicinity of Badajoz or Elvas, then he would have to leave a considerable portion of his own force south of the Tagus.

The principal French effort, nevertheless, would almost inevitably be delivered north of the Tagus somewhere along the ninety or so miles of the Beira frontier. This district, between the Douro and the Tagus, was land that Wellington had only a limited knowledge of, but he had ordered the entire area to be carefully mapped. By the winter of 1810 most of Central Portugal had been accurately mapped on a scale of four miles to the inch.

The information was gathered from a variety of sources, but mainly from the reconnaissance made by specifically employed 'exploring officers'. The Beira frontier is divided into two by the Serra de Estrella which crosses the border line at right angles, halfway between the Douro and the Tagus. The passes either side of the Estrella were described by Wellington as 'two great entrances into Portugal'. An invader must make his advance either to the south or to the north of the Serra. To attempt to march his army on both sides of the range would leave the two columns completely separated.

South of the Estrella, through Coria, were two routes. One ran through the mountains of the Sobriera. Formosa, the other via Castello Branco, Abrantes and the valley of the Tagus. It was along the first of these routes that Junot invaded Portugal in the winter of 1807-8. This road was the worst that could be found between the Serra da Estrella and the Tagus. Even though Junot's march had been unopposed he lost many men on the way and eventually he had to leave behind his artillery.

Along this route there were long stretches where water was difficult to find. Parts of the main road were so steep that to move a sixpounder (by no means the heaviest of field ordnance) required not only a dozen horses but also the assistance of fifty men. Junot's experience served as a warning to the other French generals and this road was never used again for an advance against the Portuguese capital. The second route was a likely avenue for the invaders to take. It would probably have involved the French having to force the passage of the Zezere river in the face of the defending army. It would certainly have entailed besieging the fortress of Abrantes.

There were actually two roads that ran east of the Zezere, the old Castello Branco road and the new by-road, the Estrada Nova. If the French were to invade in this direction it would be along the Estrada Nova that they would march. This was in spite of the fact that it ran along an absolutely uninhabited mountain-side where for long sections along its length water was completely unobtainable. Even though Wellington doubted that the French would use this road he decided to completely eliminate it from all consideration by destroying it. He ordered the road to be blasted with gunpowder along several points where the track passed along deep precipices. At these points the whole roadway was blown or shovelled down into the gulf below rendering it absolutely impassable for guns and wagons. [9]

Companies of irregular troops were stationed at each point to hinder any attempts by the French to repair the road.

North of the Estrella, through Ciudad Rodrigo and Almeida, were three routes: one by the valley of the Douro and two by the valley of the Mondego. The route by the Douro ran through Pinhel and Lamego and led only to Oporto and Northern Portugal, and could be of no practical use to an invading army aiming for Lisbon. This left just two roads for the French to take, both of which ran into Coimbra, one north of the Mondego, the other to the south of that river.

So although Wellington had some 400 miles of frontier to defend, there was no doubt in his mind that the main French advance would be made along either of these two roads. Although these roads crossed some difficult ground, they also ran through areas of cultivated land and a number of villages. Of the two, the route south of the Mondego, through Celorico and Ponte de Murcella, was far superior to the Celorico-Viseu-Coimbra road, and was also considerably shorter. Both of these two roads offered Wellington a choice of good defensive positions. The northerly route crossed the high granite ridge of the Serra de Busaco, which was one of the most formidable positions in the whole of Northern Portugal. The southern route, the one that Wellington firmly believed the French would follow, contracted into a difficult defile at the Ponte de Murcella over the River Alva. The Busaco heights required no strengthening. At Ponte de Murcella, however, Wellington ordered the construction of a line of earthwork redoubts. It was here that he calculated that he would 'fight a battle to save the country.' [10]

The River Mondego just above Penacova where the River Alva joins the Mondego, from the South-East. To the North-West rises the heights of Busaco.

Wellington was not simply going to chance everything on a single pitched battle however, despite the strength of the defences he was building at Ponte de Murcella. 'I have fought battles enough,' he told Sir Charles Stuart, 'to know that even under the best arrangements, the result of any one is not certain'. [11]

The position on the Alva could also be turned from the south by an invading army crossing the Tagus. So although Wellington hoped to be able to stop the French at Ponte de Murcella, he had to find further defensive positions below the point where the Tagus could be crossed. He knew that the most important consideration was the defence of Lisbon. 'In case the enemy should make a serious attack upon Portugal, 'Wellington wrote to Admiral Berkeley, who commanded the British squadron in the Tagus, 'his object, as well as that of the allies, would be the possession of the city of Lisbon'.

Wellington was prepared to give up the rest of the country to the invaders in order to 'confine ourselves to the preservation of that which is most important - the capital. [12]

Although Wellington hoped to be able to hold the French at Ponte de Murcella, his final stand would, in all probability, be in front of Lisbon. At Torres Vedras, less than thirty miles north of the capital, would be built the great line of fortifications that would defy the mighty legions of the Emperor Napoleon.

The Lines of Torres Vedras, though they were the most important and elaborate feature of Wellington's strategic plans, were only part of a completely integrated defensive policy. This included the re-organisation of the Portuguese Regular Army and the mustering of the militia, together with the revival of the ancient call to arms of the Ordenanza. It also required the destruction or removal of every commodity that would be useful to the enemy. The organisation and implementation of these schemes, however, would require time, and the more time that Wellington had the more complete would be his arrangements. Fortunately, the military situation in Spain encouraged Wellington to believe that he would be granted the time he so desperately needed.

French Invasion of Portugal Part 1: Wellington's Plans for the Defence of Portugal

Introduction
The Military Geography of Portugal
The Situation in 1810 and Fortresses
The Devastation of the Countryside and Footnotes