by Ed Whelan, Contributing Writer, Classical Wisdom
Ancient religion was very dynamic and evolved over the centuries. One of the most interesting examples of this is the Triad of Artemis, or the Triple Goddess, wherein three goddesses were conflated or grouped together. These three goddesses were Artemis, Selene and Hecate.
The group is frequently known in modern times as the Artemis Triad.  But in Graeco-Roman civilization, the Triad was known by a variety of different names.  Artemis is one of the Olympian gods and was the patron deity of hunting, wildlife, virginity, and the Moon. She was revered as the protector of women and children and for her healing powers. She was a daughter of Zeus and was also known as the virgin goddess.
Selene (or Cynthia) was another lunar deity and was believed to embody the Moon.  She was the daughter of Titans, and her siblings included Helios, god of the sun and Eos, the dawn. Selene was thought to drive her silver chariot across the skies at night, which represented the moon. Her partner was Endymion with whom she had up to 50 daughters. She was often represented with horns, which are thought to represent the Moon in its waning crescent phase.
Selene from a Roman-era burial vault
Selene from a Roman-era burial vault
Hecate was an ancient Greek goddess, and she is associated with borders, barriers and crossroads, as well as night, magic and witchcraft. She was deeply associated with the world of spirits, ghosts, and the Underworld. Many sources depict witches worshipping her. Originally, she may have been a Chthonic goddess of non-Greek origin.
The Origins of the Triad
In Classical and Hellenistic religion, this trio of goddesses were very popular and appear to have been part of the public religion of Rome in particular. They were often worshipped by women; they were seen as being very well-disposed to mothers and their children. Artemis was one of the most popular goddesses in the Hellenic world, and there were many temples and festivals held in her honour. Similarly, there were shrines to Hecate at many entrances. 
The Romans adopted many Greek deities including this trio of goddesses. They worshipped Selene under the name of Luna, Artemis was known as Diana, and Hecate was referred to as Trivia. At some point, the Romans began to conflate the three goddesses, possibly in the Republican era based on images on coins. This was because the three shared many characteristics. Most prominently, all three were female and associated with the moon. They were thought to protect or favor those who invoked them. The Triad is part of a tradition of Triple-deities that are common in mythologies around the globe. Some believe that the grouping of the Goddesses in a Triad reflects the influence of Celtic Mythology, but this is controversial.
Artemis (Diana) as the huntress
Artemis (Diana) as the huntress
The Worship of Hekate-Artemis-Selene
Much of what we know about the Triad of goddesses comes from Roman-era period from the (1st-5th century AD). References to the goddesses are made by Seneca the Younger, as well as the epic poets Statius and Nonnus.  From these we can see that the Triad of Artemis-Selene-Hecate was often worshipped in groves, which were believed to be sacred to Artemis. It appears that the Triad was also worshipped at shrines sacred to Hecate and Selene. The Triad was believed to have the combined attributes and powers of all three of the goddesses. In the Roman era, they were regarded as the protector of travellers, and associated with the world of the spirits. In the tragedy Phaedra by Seneca, the heroine prays to the Triad to make her beloved return her love. 
It should be noted that the worship of the Triad did not mean that the individual goddesses lost their identity or role in Graeco-Roman religion. They were often known as Hecate the triple goddess, or three-faced Selene and worshipped as a group because of their close-associations and were not viewed as a single divinity.
The triad and magic
It appears that the Triad was very popular with magicians and those who practised magic, which was ubiquitous in the ancient world. This is evident from surviving papyri that have been unearthed in the deserts of Egypt, which record magical incantations and spells. There are many references to Hecate in her triple aspect in surviving Graeco-Roman magical papyri, and specific references to her as being part of the Triad. Hecate was associated with magic and witches, while Selene and Artemis were associated with the moon and night. The trio my have been conflated and grouped together to make a spell more efficacious and this became a convention.
Triads of gods were very common in the ancient world. Hecate-Selene-Artemis were not aspects of the same god but were worshipped as a group because of their similarities. The conflation of the deities was most common during the Roman era especially during the Empire. The triad was very popular, and it appears that based on ancient magical papyri, that the group of goddesses were important in witchcraft and magic.
Burkert, Walter (2000). Greek Religion. Blackwell Publishers: London.