European governments have invoked the collective defence clause of Nato's founding treaty for the first time.

BBC: EU sidelined by US

Nato ambassadors invoked a mutual defence clause in the organisation's founding treaty for the first time in its history.

BBC: Bush calls attacks 'acts of war'

The founding Treaty of Rome was signed the very next year, in 1957.

ECONOMIST: The Suez crisis

The founding EU Treaty prevents eurozone member states from taking on each other's debts - meaning that even if the will for a bailout was unanimous, it would be legally tricky to accomplish.

BBC: Greece on a knife-edge ahead of euro-crisis meeting

As a mark of pride, every Italian government ritually reminds its partners abroad that Italy was a founding signatory of the treaty that ushered in what became the European Community, and Rome its birthplace.

ECONOMIST: Charlemagne

NATO's own founding document, the 1949 North Atlantic Treaty.

ECONOMIST: Law and right: When they don’t fit together | The