The Lines of Torres Vedras

Built in secret by the British to protect Lisbon from land-based attack, the lines of Torres Vedras stretched from the Atlantic coast to the banks of the impassable Tagus River.

It took 10,000 labourers a year to complete and cost some 100,000 pounds. That figure is not surprising in that the triple defensive lines consisted of more than 100 redoubts packed with almost 450 cannons.

More than 25,000 troops, mainly militia, garrisoned the lines and signal stations on dominant mountain tops meant a message could be transmitted from one end of the positions to the other in under seven minutes.