[quincunx]

Looked up the significance of that date for Portugal:

Freedom Day (25 April) is a national holiday, with state-sponsored and spontaneous commemorations of the civil liberties and political freedoms achieved after the revolution. It commemorates the 25 April 1974 coup and Portugal's first free elections on that date the following year.

Nice bridge.

[andresp]

The original name of the bridge was "Ponte Salazar". Salazar was the dictator that was leading the country when the bridge was built (60s). After the revolution, the government changed the name to "Ponte 25 de Abril" (date of the revolution as you mentioned).