light half of the year started at Calan Haf/Bealtaine (around 1 May, modern calendar). This observance of festivals beginning the evening before the festival day is still seen in the celebrations and folkloric practices among the Gaels, such as the traditions of Oíche Shamhna (Samhain Eve) among the Irish and Oidhche Shamhna among the Scots. Julius Caesar said in his Gallic Wars: "[the Gaulish Celts] keep birthdays and the beginnings of months and years in such an order that the day follows the night." Longer periods were reckoned in nights, as in the surviving English term fortnight meaning two weeks, and the obsolete se'nnight meaning one week. The Laws of Hywel Dda (in editions surviving from the 12th and 13th centuries) make repeated references to periods of nine days (nawfed dydd), rather than the "eight nights" that make up the current word wythnos. Native calendar terms in Celtic languages Many calendrical and time-keeping terms used in the medieval and modern Celtic languages were borrowed from Latin and reflect the influence of Roman culture and Christianity on the Insular Celts. The words borrowed include the month names Januarius (Old Irish , Irish Eanáir, Welsh ), Februarius (Old Irish , Irish Feabhra, Welsh ), Martius (Old Irish , Welsh ), Aprilius (Old Irish , Irish Aibreán, Welsh ), Maius (Welsh ), Augustus (Old Irish , Welsh ); the names for the days of the week, Solis, Lunae, Martis, Mercurii, Jovis, Veneris, Saturni; the terms septimana "week" (Old Irish , Breton , Cornish ), kalendae "first day of the month" (Old Irish , Welsh , Breton ), tempore "time" (Welsh ), matutina "morning" (Cornish , Irish maidin), vespera "evening", nona "noon" (Welsh , Irish nóin), and ôra "hour" (Welsh , Breton , Irish uair). A number of native Celtic terms survived the adoption of the Roman/Christian calendar, however: In Neopaganism In some Neopagan religions, a "Celtic calendar" loosely based on that of Medieval Ireland is observed for purposes of ritual. Adherents of Reconstructionist traditions may celebrate the four Gaelic festivals of Samhain, Imbolc, Beltane, and Lughnasadh. Some eclectic Neopagans, such as Wiccans, combine the Gaelic fire festivals with solstices and equinox celebrations derived from non-Celtic cultures to produce the Wiccan modern Wheel of the Year. Some eclectic Neopagans are also influenced by Robert Graves' "Celtic Tree Calendar", which has no foundation in historical calendars or actual ancient Celtic Astrology, instead being derived from