“Nemetona’s themes are wishes, protection, joy, fairies, magic, luck and nature. Her symbols are Hawthorn trees (or trees in general). In Romano-Celtic regions, Nemetona guards groves of trees with a special protective presence that marks the area as a sacred site. Within this space, the soul is hushed and calm, becoming one with nature and the Goddess. Nemetona’s name means ‘shrine’ giving new depth of meaning to William Cullen Bryant’s poetic phrase ‘the groves were God’s first temples.’
‘Bawming the Thorn‘ is a ritual that takes place around this time of year in Appleton, England. It is an occasion for the community to gather together and decorate a hawthorn tree in the center of town. Local people believe this was a spot of ancient Pagan worship, which is highly likely since hawthorns are sacred to both witches and fairy-kind. In magic traditions, carrying a hawthorn ensures happiness and promotes good luck (not to mention bearing a bit of Nemetona with you). Wherever the oak, ash and thorn grow together is a very magical spot filled with Nemetona’s power and one that will be visited regularly by fairies!”
(Patricia Telesco, “365 Goddess: a daily guide to the magic and inspiration of the goddess”.)
Patricia Monaghan tells us that Nemetona was “the British ‘Goddess of the sacred grove’ as one of the divinities worshiped at Bath, where Sul was honored as patron of the thermal springs. Nemetona was depicted as a seated queen holding a scepter, surrounded by three hooded figures and a ram” (p. 228).
I found what Sora Nalani wrote to be very informative and inspiring: “A Continental Deity revered during Roman times; Her name may be cognate with the Irish Valkyrie Nemain, and in fact the Romans seem to have regarded Her as having some connection with Mars.” 
“Nemetona is a very ancient Goddess of the Celts, specifically those in Gaul (what is now France). As well, She is thought to have been the eponymous deity of the Nemetes, a group of Germano-Celtic people living by the Rhine in an area now called Trier in Germany. The Celts, in general, did not build temples, but rather practiced their spirituality in sacred groves and Nemetona personifies this belief in the sacred land. Her name literally means ‘sacred space’, from the Celtic root ‘nemeto’ which means ‘sacred area’. She is related to the druidic concept of nemeton, the designation of sacred spiritual space.
Nemetona was worshipped primarily in what is now France and Germany, but Her worship extended into England, where there is an altar dedicated to Her in Bath. Her name survives through many place names including Augustonemeton (France), Nemetacum/Nemetocerna Atrebatum (Northern France), Nemetobriga, Nemetodurum (modern Vernantes), Nemetatae (A tribe in Northern Spain), Nemetostatio (England), Vernenetum and Medionemeton (both in England).
Inscriptions found have shown that the Romans afflicated Nemetona with Mars. In Trier and Altrip, in Germany, inscriptions have been found pairing Her with Mars specifically and in Bath with Loucetios Mars. It is well know that as the Romans spread through the Celtic world that they paired their deities with the local deities, finding commonalities. Loucetios was a storm god, the divine mate of Nemetona, whose name means ‘bright’ or ‘shining one’. It is thought that he may be the original form of Lleu/Lugh, the Welsh god of light. With Lugh figuring as a ‘divine warrior’ in many myths, it makes a certain sense that the Romans would equate Loucetios with their god of war, Mars. Still, the fit is awkward and does little to retain the original power and meaning of both Nemetona and Her consort. As is often the case with the Roman deity overlays, it seems as if there was some breakdown of communication as the Romans tried to fit their war hungry gods over the more shamanistic gods of the Celts.”
Sora Nalani goes on to say: “At first I had found the fit of Nemetona and that of Mars to be almost ridiculous, it just didn’t seem as if it could be. But when I found a pairing of her with the Brythonic God, Mars Rigonemetis ‘King of the sacred grove’, a new picture began to form in my mind, one of a year King associated with the sacred Goddess whose tendrils of energy were inseparable from the land. It is very possible that Rigonemetis was the guardian of the sacred grove, the guardian of the sacred mother and wellspring of life; Nemetona. I then read that the Celtic ‘Mars’ was a god of protection and healing, along with agriculture in addition to the war-like aspects. Even Loucetios, a lightening god, is associated with sacred groves, as the druids associated lightening with sacred trees, in particular oaks. It is very possible the Loucetios would have been associated with ‘drunemeton‘: the sacred oak grove.
It seems a cruel twist of fate that some think She survives on as Nemhain, the Irish Goddess of battle frenzy . While the path from Goddess of the groves to the Goddess of the battlefield is not so farfetched through Her association with Her divine consort who inevitable was linked with Mars, the god of war, the pairing of Nemetona and Nemhain seems little more than a construct of similarity in names rather than an real evolution of Goddess worship.
I could not find many images of Nemetona but in the surviving iconography, She is pictured seated, holding a scepter surrounded by 3 hooded figures and a ram. This portrayal feels more Roman than it does Celtic, it seems more likely to me that her presence would have been found in the spiraling knotwork and the labyrinth iconology of the Celts.
Nemetona is a difficult Goddess to wrap my mind around. She is somewhat nebulous in my mind, partially because She seems inextricably linked with the land. She is the sacred grove and it is Her. She is sacred space, whether that is found within the majestic trees of a grove or if it is held simply within one’s heart. She is holy breath, the sanctuaries we create, not out of stone and mortar, but out of love and reverence. She is a sacred link between ourselves and the living planet. But in my mind, not in an all-consuming way, such as a deity like Gaia, but in a very personal , intimate way, our link to the land our feet walk on, to the trees our ears hear singing in the wind and the leaves that season with us. She is the animation of the living space around us, a reminder to create that which is sacred within and carry it through all our trials and journeys. She is the circle unto herself and we are within Her circle, found within our relationship with our most intimate and immediate environments. She is the wholeness within each single leaf on the plant that sits beside you, or the moving cells of your body, and the embodiment of all personal spiritual cycles. Simply put, she is sacred space.” 
Other names: Nemetonia, Nemetialis
Joelle’s Sacred Grove, “Celtic Gods and Goddesses“.
Monaghan, Patricia. The New Book of Goddesses and Heroines, “Nemetona”.
Nalani, Sora. Spira, “Nemetona: Goddess of the Sacred Grove“.
Eagle Feather, Lavender. The Simplified Witch, “Goddess Guidance…Nemetona”
Nemeton – the Sacred Grove: Home of the Celtic gods, “Nemetona: A Gaulish and Brythonic Goddess (She of the Sacred Grove)“.