Chamomile flowers, Chamaemelum nobile, have been used for many centuries, most likely from before the Roman occupation.
Infuse the flowers, into a teapot, for between 3 - 5 minutes to produce a soothing drink used to calm abdominal pains, nervous upsets, and rheumatism. Apparently, this herbal tea also “eases insomnia, boosts your immune system, and banishes menstrual cramps.” A cup a day is said to keep colds at bay by supporting your immune system, as Beatrix Potter says in The Tale of Peter Rabbit; when Peter was unwell during the evening; his mother put him to bed, and made some chamomile tea: "One table-spoonful to be taken at bed-time."
It goes without saying that if you're pregnant (or are under the doc for anything) caution should be exercised with herbal decoctions.