Trisagion prayers

[futureKC123]

+JMJ
Where exactly do our beloved trisagion prayers originate?
Thanks,
FKC

 

[ConstantineTG]

kiev-orthodox.org/site/english/639/

After the fourth century, other elements were gradually added. One of these elements is the chant of the Trisagion.
The Trisagion was an old troparion sung during penitential processions. In the fifth century it was not uncommon to hold penitential processions through the city of Constantinople, to entreat God to protect the town from earthquakes and other calamities. The legend about the origin of the Trisagion actually connects the revelation of this hymn with an earthquake that struck the capital before 450 A. D.
According to this legend, the earthquake was catastrophic, and the people gathered in prayer outside the town, asking God to have mercy upon them: Kyrie, eleison (Lord, have mercy). Suddenly a boy was taken up into heaven, where lie heard the chant of the angels: «Holy is God, Holy and Mighty, Holy and Immortal Have mercy on us!» The boy returned to earth and told the crowd what the angels were singing; at this, the people themselves started singing the same chant, the Trisagion, and the earthquake ceased.
And thereafter, the Trisagion was sung in penitential processions, which went from one church to another where the Liturgy was then celebrated. Before it arrived at the second church, the procession would make one or several stops at appointed stations, to pray to God for the special favor sought. One customary station was the Forum of Constantinople, a large plaza in the town. Here was recited a special prayer, the Ectenes or Insistent Litany, which later was incorporated into the Liturgy itself. Sometimes, the patriarch himself recited other prayers asking God to protect the town. On the most solemn occasions, such as the beginning of the year (September 1st) or the anniversary of the foundation of the city (May 11th), three antiphons were sung; these were followed by the reading of the Epistle and Gospel. The Insistent Litany (ectenes) ended the prayer at the station, and the procession moved towards the church singing a psalm with a troparion repeated after each verse.
In ancient times, the Troparion sung on the way to the church was the Trisagion itself, repeated by the people after each verse of the chosen psalm. This was usually, it seems, Psalm 79 (80): «Give ear, O shepherd of Israel, thou who leadest Joseph like a flock,» because to the present day the bishop sings, intercalated with the Trisagion, verses 14-15, of this same psalm:
Turn again, O God of hosts! look down from heaven and see; have regard for this vine, the stock which thy right hand planted.
Before the procession started from the first church, the «Prayer of the Trisagion» was recited by the patriarch. From its text we can see its relationship to a procession of penance:
… you do not despise the sinner, but ordain repentance for his salvation … accept, O Master, from the lips of us sinners the thrice-holy hymn, and deal with us according to your kindness: forgive us every offense, whether of malice or of weakness, sanctify our souls and bodies, and grant that we may serve you in holiness all the days of our life …
At the end of the procession, as it entered the second church, the singers, to conclude the psalm, intoned the «Glory be to the Father, etc.,» and the Trisagion was repeated twice more. This explains why today the Trisagion is repeated after the «Glory be to the Father.» Then, once the procession was inside the second church, the Liturgy began as usual with the celebrant’s greeting to the people: «Peace be to all,» and the scriptural readings.
THE TRISAGION INCORPORATED INTO THE LITURGY
Thus we see that formerly the Trisagion was sung during special processions. But the sixth century documents from Constantinople show us that even on days when there was no procession, the Trisagion was sung. When the clergy made their entrance into the church for the celebration of the Liturgy, the Trisagion was used as the entrance hymn. A new element then, formerly belonging to the processions, had been incorporated into the Liturgy.
Along with the Trisagion, but probably in a later epoch, two other pieces were taken from the processions and added to the Liturgy: the prayer before the Trisagion, and the Insistent Litany, which was placed after the reading of the Gospel, just as it was during the station at the Forum—on special occasions.

 

[ThatOneGuy92]

kiev-orthodox.org/site/english/639/

That is pretty much a good summary. To note- it is likely older than the 4th century.