The dalmatikon is a long outer vestment almost to the floor. It is fastened at the sides with loops and baubles. Usually edged in gold and carrying ecclesiastical motifs, it can be the colour of the day, and highly decorated.
The deacon drapes the orarion over the top of it.
Subdeacons also wear a dalmatikon but with shorter crossed orarion.
In the fourth century the imperial vestment, the dalmatikon, so named after the area from which it originated, started to be used in the universal Church. The emperor granted the right to wear a dalmatikon to particular high officials within the imperial bureacracy, and later extended the right to particular bishops, and some highly favoured deacons.
Over time, the dalmatikon came to be recognised as the vestment of bishops in favour with the emperor. When specific deacons were granted the right to wear the dalmatikon they were recognised as representing the emperor, or a highly favoured bishop.
Over the next few centuries, the dalmatikon then came to especially symobolise the archbishop's primary helpers, the patriarchal deacons. Still later it was adopted as the usual liturgical vestment of all deacons, both east and west.
As part of the enormous upheavals in the eastern Church caused by the fall of Constantinople in 1453, the Church had thrust upon it the worldly responsibilities formerly exercised by the emperor over his Christian subjects. The Ottoman overlords made the bishops responsible for the material government of their own people, as well as the spiritual responsibility they had always exercised.
It was from this time that the eastern bishops relinquished the use of the divided mitre still seen in the western church today, and adopted the imperial crown as their episcopal headgear.
It was also from this period that the use of the word dalmatikon began to disappear from the liturgical vocabulary to be supplanted by a widened meaning of sticharion.
Today some jurisdictions still use the older word dalmatikon for the deacon's outer liturgical vestment, but most jurisdictions use the more generic term sticharion.