The feast is an optional memorial for June 30th and celebrates the first Christians martyred during the persecution of Nero in 64 AD against the Christians living in the city. The martyrdom was recorded by both Tacitus and Pope Clement I. In July of 64, a terrible fire broke out and devastated much of the city. When the tragedy began to be blamed on Nero due to construction involved enlarging his palace he turned and placed the blame squarely at the Christian community in the city. Tacitus recorded the martyrdom :
Covered with the skins of beasts, they were torn by dogs and perished, or were nailed to crosses, or were doomed to the flames and burnt, to serve as a nightly illumination, when daylight had expired. Nero offered his gardens for the spectacle, and was exhibiting a show in the circus, while he mingled with the people in the dress of a charioteer or stood aloft on a car. Hence, even for criminals who deserved extreme and exemplary punishment, there arose a feeling of compassion; for it was not, as it seemed, for the public good, but to glut one man's cruelty, that they were being destroyed.
The feast was first placed into the General Roman Calendar during the 1969 reforms to give a celebration to the early Roman martyrs. This feast replaced many other Roman martyr feasts that had been held throughout the year and was placed directly after the Solemnity of Saints Peter and Paul.