To this day, the country is still reeling from that default.

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In turn, the country's departure from the eurozone would "result in widespread default on private sector as well as sovereign euro-denominated obligations, " the ratings agency said.

CNN: Spain faces bank concerns after downgrade

And Neil Mackinnon, chief economist at VTB Capital, said the future for Greece is far from clear, adding that it was "now probable" that the country would default.

BBC: Greek debt default 'now probable'

Stressing the need to learn lessons from the crisis, she wants a treaty change to allow sanctions to come into force should a eurozone country ever default on its debts.

BBC: Merkel praises eurozone deal to help Greece