Submitted by Hugo Palma:
The Lines of Torres Vedras was a military defensive system, constructed to the north of Lisbon between 1809 and 1810. Under a cloak of secrecy, the future Duke of Wellington developed a defence strategy based on the fortification of key points on the hilltops so as to be able to observe the access routes to the capital of Portugal and reinforce the natural obstacles of the local terrain. This system comprised three lines of defence, extending over 85 km from the Atlantic to the river Tagus.
When finished, there were 152 military constructions, armed with 600 artillery pieces and defended by 140,000 men, making it the most efficient – as well as the cheapest – defensive system in military history.
The GR 30 is a pedestrian route created in the context of the Lines of Torres Vedras that crosses 6 of its municipalities and also goes through most of the military edifications constructed at the time. It is a loop of about 88km.