When a raiding party from Islamic State of Iraq and the Levant attacked a Saudi border post last week, it was no mere hit on a desert outpost.

The jihadists were launching an assault on the new, highest profile effort by Saudi Arabia to insulate itself from the chaos engulfing its neighbours.

The Saudis are building a 600-mile-long “Great Wall” – a combined fence and ditch – to separates the country from Iraq to the north. […]