According to the legends St. Cecilia was born in Rome to a senatorial family. She was raised as a Christian from infancy and was well educated.
The young Cecilia vowed secretly to maintain her virginity and to dedicate her life to serving Christ as His bride, but her parents forced her into an arranged marriage with a nobleman named Valerian. She maintained her distance through the wedding ceremony, and while the musicians at the celebration played pagan songs, she sang to God in her heart in honor of her avowed spouse. This is why she is the patron of musicians and liturgical music.
She informed her new husband of her secret vow, which to his eternal credit, he respected. She converted him to Christianity and he was baptized by Pope St. Urban I. Valerian and his brother, who the couple subsequently converted, dedicated their lives to Christ by buying the remains of martyred Christians and giving them proper burials. The brothers were arrested and condemned as Christians and were sentences to scourging and beheading. During their time under the whip they managed to convert an officer named Maximus who was assigned to guard them, and the three men were beheaded together.
Cecilia retrieved their remains and buried them after which she was brought to the attention of the authorities as a Christian. Those who were sent to her in order to compel her to sacrfice to the pagan gods were themselves converted by Cecilia, over 400 souls on one occasion.
Cecilia was brought before the authorities and after a heated argument was sentenced to be asphyxiated by being locked in her bathroom with the fires used to heat the bath and create steam stoked up to several times their normal temperature. She was discovered to be unharmed after a lengthy period and the order was given to remove her head. Her inept executioner failed at his task even after three blows and she was left to die, bleeding, on the ground. Many people came to visit her while she lay dying, including the Pope Urban, to whom she bequeathed her property to the Church. She was buried in the Catacombs on the Appian Way
Though nothing can be shown to be historically accurate in the legends surrounding the life and martyrdom of St. Cecilia, there was definitely a wealthy roman Christian woman who was martyred around the time of Pope St. Urban I, and buried in the Catacomb of Callistus on the Via Appia. A church was built in the fourth century dedicated to St. Cecilia in the fifth century. It was common practice to dedicate early Roman churches to sainted benefactors who donated land and/or buildings to the Church, and it has been shown that the land most likely belonged to her family.
There were also three other martyrs named Valerianus, Tiburtius, and Maximus were buried together in the Catacomb of Praetextatus on the Via Appia near the same time. The details of their relationship may or may not be accurate. The story of their martyrdom was written centuries later and may have been romanticized and expanded to tie their lives together.
In the "Sacramentarium Leoniam", a collection of Masses written about the end of the fifth century, there are five different Masses in honor of St. Cecilia, indicating that she was held in great veneration at that time by the Roman Church.
From the Catholic Encyclopedia:
Her church in the Trastevere quarter of Rome was rebuilt by Paschal I (817-824), on which occasion the pope wished to transfer thither her relics; at first, however, he could not find them and believed that they had been stolen by the Lombards. In a vision he saw St. Cecilia, who exhorted him to continue his search, as he had already been very near to her, i.e. near her grave. He therefore renewed his quest; and soon the body of the martyr, draped in costly stuffs of gold brocade and with the cloths soaked in her blood at her feet, was actually found in the Catacomb of PrŠtextatus. They may have been transported thither from the Catacomb of Callistus to save them from earlier depredations of the Lombards in the vicinity of Rome. The relics of St. Cecilia with those of Valerianus, Tiburtius, and Maximus, also those of Popes Urbanus and Lucius, were taken up by Pope Paschal, and reburied under the high altar of St Cecilia in Trastevere. The monks of a convent founded in the neighbourhood by the same pope were charged with the duty of singing the daily Office in this basilica. From this time the veneration of the holy martyr continued to spread, and numerous churches were dedicated to her. During the restoration of the church in the year 1599 Cardinal Sfondrato had the high altar examined and found under it the sarcophagi, with the relics of the saints, that Pope Paschal had transported thither. Recent excavations beneath the church, executed at the instigation and expense of Cardinal Rampolla, disclosed remains of Roman buildings, which have remained accessible. A richly adorned underground chapel was built beneath the middle aisle, and in it a latticed window, opening over the altar, allows a view of the receptacles in which the bones of the saints repose. In a side chapel of the church there have long been shown the remains of the bath in which, according to the Acts, Cecilia was put to death.
"In the midst of the concert of instruments, the virgin Cecilia sang to God alone in her heart: 'May my heart and my body remain pure, O God. Let me not be confounded.'
"She imposed on herself fasts of three and four days. She prayed and gave into God's keeping that for which she feared.
"Saint Cecilia, you triumphed over Almachius, the prefect, and converted two brothers by showing them bishop Urban of the angelic face. Like an industrious bee, you served the Lord.
"The glorious virgin forever carried the Gospel in her heart. Day and night she prayed and communed with God. She stretched out her hands to the Lord. Her heart was on fire with heavenly love.
"With her hairshirt, Cecilia subdued her body. She groaned and cried out to God. She brought Tiburtius and Valerian to share the crown. She was a wise virgin, to be numbered among the discreet.
"O Lord Jesus Christ, our good Shepherd, author of chaste vows, receive the fruit of the seed that you sowed in Saint Cecilia. Your servant Cecilia, like an industrious bee, spent herself in your service. The husband that came to her like a fierce lion, she brought to you like a most gentle lamb.
"There is a secret, Valerian, that I wish to tell you: 'I have as my friend an angel of God who watches over my body with jealous care.
"Saint Cecilia said to Tiburtius: 'Today I greet you as my brother, for the love of God has made you spurn idols.'
"We believe that Christ, the son of God, who chose unto himself such a servant, is the true God.
"As the dawn was breaking, Cecilia cried: 'Awake, soldiers of Christ. Cast away the works of darkness and clothe yourselves with the arms of light.
"I asked the Lord to spare me yet for three days that I might consecrate my house as a church."