My source is the Catholic Encyclopedia, although I have taken out some of the bias that the 1907 writers put into the discussion.
It was an ordained ministry.
From the 4th century Apostolic Constitutions (a document whihc is Roman but seeme to have some eastern elements in it:
Concerning a deaconess, I, Bartholomew enjoin O Bishop, thou shalt lay thy hands upon her with all the Presbytery and the Deacons and the Deaconesses and thou shalt say: Eternal God, the Father of Our Lord Jesus Christ, the creator of man and woman, that didst fill with the Spirit Mary and Deborah, and Anna and Huldah, that didst not disdain that thine only begotten Son should be born of a woman; Thou that in the tabernacle of witness and in the temple didst appoint women guardians of thy holy gates: Do thou now look on this thy handmaid, who is appointed unto the office of a Deaconess and grant unto her the Holy Spirit, and cleanse her from all pollution of the flesh and of the spirit, that she may worthily accomplish the work committed unto her, to thy glory and the praise of thy Christ.
The Catholic Encyclopedia discusses the fact that bishops in the early church did argue themselves as to whether this was an ordained ministry or not, and refers to some obscure councils the opinion that it was not an ordained ministry. The EC's arguments are not all that strong.
What did they do?
The primary purpose of the Deaconesses was in the era of segregation of worship, with a separate mens and womens section in the church. Therefore their roles were:
- the instruction and baptism of catechumens
- guarding the doors and maintaining order amongst those of their own sex in the church,
- acting as intermediaries between the clergy and the women of the congregation.
They may have also functioned as Ministers of Holy Communion to the womens section of the church but I have not found any evidence for this.
However, the Apostolic Constitutions make it clear that "the deaconess gives no blessing, she fulfills no function of priest or deacon", So in Rome at least, their role was very different from the Deacon. For instance they did not minister at the Altar assisting the priest like a Deacon nor did they read the Gospel, sing the Ite Missa Est, or preach a homily.
However, we do hear that in the churches of Syria and Asia, of them presiding over assemblies of women, reading the Epistle and Gospel, distributing the Blessed Eucharist to nuns, lighting the candles, burning incense in the thuribles, adorning the sanctuary, and anointing the sick. This seemed to be regarded as an abuse which ecclesiastical legislation soon repressed.
If they did not function as a deacon did they have any role in the Liturgy?
Its difficult to determine where they had a place in the liturgy. A document called "Testament of Our Lord" (c. 400), widows had a place in the sanctuary during the celebration of the liturgy, they stood at the anaphora behind the presbyters, they communicated after the deacons, and before the readers and subdeacons, and they had a charge of, or superintendence over the deaconesses.
It is recorded that in the time of Justinian (d. 565) at the Basilica of St. Sophia in Constantinople the staff consisted of sixty priests, one hundred deacons, forty deaconesses, and ninety subdeacons. However, I cannot see any reference to them in any of the Roman legislation from the same period. One exception is the the ninth Ordo Romanus mentions, feminae diaconissae et presbyterissae quae eodem die benedicantur. Diaconissae are also mentioned in the procession of Leo III in the ninth century
When did they die out?
The ministry seemed to have died out when just about everyone was Christian and adult baptism had practically died out. Balsamon, Patriarch of Antioch about A.D. 1070 states that deaconesses in any proper sense had ceased to exist in the Church though the title was borne by certain nuns while Matthew Blastares (c 14th cent) said that by the the tenth century that the civil legislation (presumably that of the eastern Roman Empire) concerning deaconesses, which ranked them rather among the clergy than the laity had then been abandoned or forgotten.
The only surviving relic of the ordination of deaconesses in the West (and this may have disappeared after Vatican II) was the conferring of a stole and maniple to Carthusian nuns in the ceremony of their profession.
Could they be revived?
The short answer is probably not as the need for the role has disappeared (men and women worship together and there is no modesty issues around baptism) and laity (whether men or women) can provide leadership in these areas. It needs to be kept in mind that the role was never an Altar ministry.
All this been said, it gives an interesting overview to the fact that the Church saw it as an ordained ministry, and that ordination to specific non priestly roles could be opened to everyone.