For 10 points, name this South American city located across the Rio de la Plata from Uruguay, the capital of Argentina.
This city's downtown square was historically the site of marches of the mothers of "los desaparecidos;" that square is the Plaza de Mayo. The Teatro Colón and Casa Rosada are found in this city whose residents are called porteños. This city is the capital of a country that claims ownership of the British-controlled Falkland Islands. For 10 points, name this South American city located across the Rio de la Plata from Uruguay, the capital of Argentina.
This city's downtown square was historically the site of marches of the mothers of "los desaparecidos;" that square is the Plaza de Mayo.
{Buenos Aires}