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The flag of Buenos Aires, the capital of Argentina was originally designed in 1580, but it was officially adopted on October 24, 1995. It shows the coat of arms of the House of Habsburg, as the flag has an eagle on a white background. The use of Habsburg symbols comes from Charles V of the Habsburg dynasty, who was king of Spain when Buenos Aires was originally founded in 1536. The city was eventually abandoned, but it was refounded in 1580, during the reign of Charles V's son, Philip II.

Source: Wikipedia