The Saudi border defences will mix physical barriers and surveillance
On the 20th anniversary of the fall of the Berlin Wall, BBC Mundo looks at barriers which are still standing - or have gone up since - around the world.
In order to defend the most powerful economy - and biggest oil reserves - of the Persian Gulf, the Saudi Kingdom's 9,000km (5,590 mile) border is currently being reinforced with one of the longest security fences in the world.
The project is being carried out at an estimated cost of $3bn (£1.8bn).
Saudi Arabia shares a border with Yemen which is about 1,500km long, and with Iraq which is 800km long.
The five other adjoining countries are Qatar, the United Arab Emirates, Oman, Kuwait and Jordan.
The high-tech project is being carried out by the security and defence consortium EADS and Al Rashid Trading & Contracting Co.
It will involve an actual physical barrier in some parts, but the less populated desert areas will have a virtual barrier comprising satellite monitoring, cameras, radar, electronic sensors, coastal detection centres and reconnaissance airships to detect intruders and send patrols.
A security fence is already in place on the Yemeni border, also built by EADS.