The emperor Constantius (Chlorus) I and his wife Theodora had six children: Flavius Dalmatius, Julius Constantius, Hannibalianus, Constantia, Anastasia, and Eutropia. Constantia's full name was Flavia Julia Constantia. The date of her birth is not known; even the relative ages of the six siblings are unknown, so that any list is rather arbitrary in order. If one accepts 293 as the year of her parents' marriage --- that date, however, has been called in question -- then one may assume that she was born at the very earliest in the following year. Nor is there direct evidence for her place of birth. But a good case can be made for Trier, since this city served as Constantius' principal residence during the years 293-306, and here, too, she must have spent her childhood years.
Late in 311 or early in 312, Constantine I, Constantia's half-brother, betrothed her to his fellow-emperor Licinius. She was then eighteen years old at most, while Licinius was more than twice her age. The marriage took place some months later, probably in February of 313, on the occasion of Constantine's meeting with Licinius in Milan. But the relationship between the two emperors was a strained one, and open hostilities, the bellum Cibalense, erupted in 316. Constantia remained at her husband's side. In about July of 315 she bore him a son named Valerius Licinianus Licinius.
A second war between Constantine and Licinius took place in 324. Licinius. was defeated twice, on July 3 at Adrianople and on September 18 at Chrysopolis, and soon thereafter surrendered to Constantine. Constantia interceded with her half- brother for the life of her husband, and Constantine spared Licinius' life, ordering him to reside at Thessalonike as a private citizen. A few months later, in the spring of 325, Constantine ordered Licinius to be executed, violating an oath which he had sworn to Constantia. A year or so later, in 326, the younger Licinius also fell victim to Constantine's wrath or suspicions.
The loss of both husband and son must have been a severe blow to Constantia and must have strained her relationship to Constantine. Nevertheless she occupied a position of honor and influence at Constantine's court, held the rank of nobilissima femina, and received Constantine's loving attention; Constantine was at her side when she died ca, 330, before reaching the age of forty. We do not know when, where, or how Constantia first embraced Christianity. We do know that Eusebius, bishop of Nicomedia from ca. 317 on, wielded considerable influence at court. On one occasion Constantia exchanged letters with the other Eusebius, bishop of Caesarea. Jerome, Rufinus, Socrates, Sozomen, and Theodoret, while not in full agreement on some of the details, all report that she was a defender of the person and doctrine of Arius. She also attended the Council of Nicaea, where she counseled the representatives of the Arian party.