SUWAYF, Saudi Arabia (AFP) - The chain-link fences, topped with coils of barbed wire, rise and fall like a serpent's back across the desert scrubland between Saudi Arabia and the militant threat across the Iraqi border.
A double-fence system and complementary high-tech surveillance tools, officially opened in September, have become the frontline of efforts to protect the kingdom from Islamic State in Iraq and Syria (ISIS) group extremists who have seized vast areas of Iraq as well as Syria.
"As you know, the terrorists are the biggest threat," said border guards Major Mohammed al-Rashidi, a supervisor at Judaidat Arar command and control centre where officers monitor radar and cameras about 10km from the frontier. That threat became painfully clear in January when three border guards including a local commander were killed in nearby Suwayf in a battle with "terrorists".
The attack followed the launch in September of the kingdom's air strikes on ISIS targets in Syria as part of a United States-led coalition. The militants have claimed responsibility for widespread atrocities, including the burning alive in a cage of a Jordanian fighter pilot.
Saudi Arabia's involvement in air strikes on ISIS targets has raised fears of retaliation by the group.
The authorities did not specifically blame ISIS for the Suwayf attack on the armed unit which protects the kingdom's land and sea frontiers.
However, the Interior Ministry has alleged three Saudis operating "in support of" ISIS shot and wounded a Danish national in a separate attack in Riyadh in November.
The authorities have also blamed ISIS-linked suspects for the November killing of seven members of the minority Shi'ite community in Eastern Province.
Border guards are taking no chances after the death of their regional commander General Odah al-Balawi and the other troopers.
"Nowadays, anybody trying to cross the border, we deal with them as terrorists," Maj Rashidi said in his command centre, one of several along the northern frontier.
That means they will be shot on sight, an order that applies all along the more than 800km border.
Maj Rashidi said they have not yet had to carry out the directive along his sector covering nearly a quarter of the frontier.
In a room resembling a small lecture hall, five officers sit at desks monitoring radar and camera feeds from the border while telephones bleep.
On one screen, a radar sweeps a green and yellow path, highlighting about 30 white dots, moving objects which could be suspicious.
An adjacent camera image, either infrared or daylight, helps the operator decide whether the objects are innocent or an "enemy" to be marked in red.
Then a message is relayed to the laptops of troopers at Rapid Response Stations in the field.
"When we have an incident we send six men, two cars," at least, Maj Rashidi said. They are armed with Heckler & Koch G3 rifles and machineguns.
Maj Rashidi's command centre and others already online have combined to create what officers call an "almost finished" northern network.
It replaces traditional patrolling on the ground to guard against smugglers and other infiltrators.
In November, the kingdom expanded a no-go zone 10km to 20km south of the border.
"It's very difficult" for anybody to cross the border now, Maj Rashidi said.
The only people allowed into the restricted zone are border guards, other government employees, and foreign labourers working with them.
Nobody else really lives in the region of yellowed, barren earth.
The paved road leading north to Iraq through the Suwayf area is flanked by barbed wire fencing and blockaded.
It once brought travellers to a sprawling walled Saudi customs compound. That was the only official crossing point but it has been closed for more than two decades.
ISIS does not control territory in southernmost Iraq but it was from there that the four attackers, all Saudis, came in January.
Cameras spotted them but when border guards went to investigate they came under fire, security officers said.
The battle ended down a bumpy track that leads from the fence to a wide, bowl-like depression in the hard ground and thorny scrub.
Here, officers say, an attacker blew himself up, killing Gen Balawi and his driver.
The weeks since have not erased the blood which has darkened the ground in a rough circle the size of a dinner plate. Spent cartridge cases and an unfired bullet lie in the nearby dirt.