The Line of Torres Vedras still preserves some of the wind mills and fortress that remain from a military defensive and observation 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 has 4 segments. This route crosses the 2 segments on the East side, with about 49K and 1650 elevation gain and crosses the East Side traverssing Socorro mountain, São Vicente fortress, and Ordasqueira fortress.
