Europe's leaders gather for a mother-of-all-summits this week under intense global pressure to head off a potentially catastrophic economic collapse.

Months ago already, European Union president Herman Van Rompuy said in off-the-cuff remarks that the eurozone stood "back to the wall", "at the edge of a cliff", "with a knife at its throat".

That was before the relentless two-year sovereign debt crisis wrecking much of Europe hit the unthinkable -- infecting Spain, the eurozone's fourth-largest economy, and threatening Italy, its third-largest, after earlier rescues of Greece, Ireland and Portugal.