Hilaria (25 March) was a day of rejoicing.
In Roman times, this was part of series of celebrations related to Cybele and Attis, representing a cycle of death and rebirth.
On the day following Dies Sanguinis the resurrection of Attis was proclaimed. This was the day of "Hilaria" or rejoicing. The first day when day is longer then night. It was a festival of Spring and life rediscovered.
There was a triumphal procession which would feature Cybele's idol; borrowed works of art; knights and senators; freedmen; flute players; trumpeters; drummers and chanters. This was followed by a lavish feasting.
Sources vary about the nature of Attis's resurrection. Some say that he was reborn as the evergreen pine; others that the body of Attis was preserved; and other more recent sources that Attis was reborn as a woman. Ultimately, the exact details don't matter that much - what matters is the idea of death and rebirth.
This was a theme in Mediterranean religions long before the spread of Christianity popularised the idea. Tammuz, Adonis, Osiris and Attis are all consorts of a Goddess, who die and yet are resurrected rather than remain dead. Some interpretations of resurrection are physical and involve an afterlife, or reincarnation. Others are emotional or spiritual, such as ego death and reconstruction, or of being "born again". Resurrections are not just simple restorations - they always involve change and alteration from what was, to what is.
Previously, we may have grieved for what should have been but wasn't, or for what has been lost and mattered. We may have also committed to a goal and sacrificed smaller desires for that goal. But there comes a time when either that goal is reached or abandoned. Either way a "death" is involved - because either way what was the goal ceases to be so any more. But it is rare that things then become static for us, that there remains a vacuum of desire in our lives - rather they change and become resurrected in new goals, ideas and ways of being. We move on and embrace further change, one way or another.
And that surely, is cause for celebration.