Rome was founded on April 21, 753 BC. We have a very long history! For us April 21st is quite an holiday: the ‘Natale di Roma’.
Each year we celebrate in the morning with an historical parade that start in the Circus Maximus, proceed along the Foro Boario, at the bottom of the Capitol, reach Venezia square and then it winds along via dei Fori Imperiali to the Colosseum and back along via di San Gregorio to the Circus Maximus.
Practically the same route of the ancient triumphal processions but in reverse.
Nothing is closed.
All Rome city museums are free on April 21. This includes Capitoline Museums, the Ara Pacis, Villa Torlonia, Trajan's Market etc. Visit the website of the Musei in Comune to see the list.