If I remember correctly from reading Eusebius' History of the Church (c324 AD), Deacons were the ones who dealt with the money and practical issues of a church community, or parish as we would say nowadays. They controlled the funds and administered the practical charity that was bought with those funds. They were responsible for standing at the door of the church to call out those known to be guilty of public sin and making sure they were either barred from Mass or were seated in the special section designed for public sinners. (This was before private Confession had been invented. Public Confession was held at Easter Vigil once a year.) They were like the administrators of the parish, whereas the Presbyter, what we now call the priest, was responsible for preaching and administering the sacraments. The Priest didn't dirty his hands with money...that was the Deacon's job.
I think that the order of Deacon was suppressed in the Renaissance because the bishops felt that the deacons had too much power in parishes and were bullying the priests.
It is interesting to me that Vatican II restored the order of Deacons, and that they are the ones supposed to be reading the Gospels, occasionally preaching, saying the Prayers of the Faithful, helping the priest distribute Holy Communion, and saying "The Mass is ended, go in peace." Rarely do I see this nowadays. Their role has been distributed among a plethora of unordained laymen. Yet one does see many good deacons administering the charity of the parish. This is a real benefit of Vatican II.
I suspect that, if our Church continues its ban on married clergy, we will see more and more parishes run by deacons in the future, with the occasional priest making the rounds to confect the Eucharist as time and distance allows. One sees this in the South Seas where there are more than a few islands with no priest available.