The Martyrs Florus and Laurus were brothers by birth not only in flesh but in spirit. They lived in the second century at Byzantium, and afterwards they settled in Illyria [now Yugoslavia]. By occupation they were stone-masons (their teachers in this craft were the Christians Proclus and Maximus, from whom also the brothers learned about life pleasing to God).

The prefect of Illyria, Likaion, sent the brothers to a nearby district for work on the construction of a pagan temple. The saints toiled at the structure, distributing to the poor the money they earned, while they kept strict fast and prayed without ceasing.

Once, the son of the local pagan-priest Mamertin carelessly approached the structure, and a chip of stone hit him in the eye, severely injuring him. Saints Florus and Laurus assured the upset father, that his son would be healed.

They brought the youth to consciousness and told him to have faith in Christ. After this, as the youth confessed Jesus Christ as the true God, the brothers prayed for him, and the eye was healed. In view of such a miracle, even the father of the youth believed in Christ.

When the construction of the temple was completed, the brothers gathered the Christians together, and going through the temple, they smashed the idols. In the eastern part of the temple they set up the holy Cross. They spent all night in prayer, illumined with heavenly light. Having learned of this, the head of the district condemned to burning the former pagan priest Mamertin and his son and 300 Christians.

The martyrs Florus and Laurus, having been sent back to the prefect Likaion, were thrown down an empty well and covered over with earth. After many years, the relics of the holy martyrs were uncovered incorrupt, and transferred to Constantinople. In the year 1200 the Novgorod pilgrim Anthony saw them. Stephen of Novgorod saw the heads of the martyrs in the Pantokrator monastery around the year 1350.

Source:

https://oca.org/saints/lives/2017/08/18/102325-martyr-laurus-of-illyria