Several calendars have been used in pre-Islamic Arabia. Inscriptions of the ancient South Arabian calendars reveal the use of a number of local calendars, as do Safaitic inscriptions from the Harran desert in Syria and Jordan. At least some of the South Arabian calendars followed the lunisolar system, while the Safaitic calendar had fixed months and seasons and, very importantly, a seasonal star calendar strongly connected to the Zodiac and the position of the ʔanwāʔ. The ʔanwāʔ, a series of asterisms on or near the zodiac belt were the most important element in pre-Islamic astronomy. These stars were connected to the season, and they were used to forecast various phenomena such as rain, temperature, wind.^[1] Before the rise of Islam, diviners invoked these stars in rainmaking rituals called istisqāʔ.^[2] Rituals took place during specific times, when the sun was in one or the other of these ʔanwāʔ, some Safaitic texts speak of ritual cleansing while the sun is in Virgo (ngm) or Sagittarius (ṯbr); another text mentions a libation during the full moon of Gemini (gml).^[3] It is thus obvious that Zodiac constellations, the position of stars and the mansion of the Sun were very important criteria and had an important impact on the pre-Islamic Arabian calendar and ritual life.

For Central Arabia, especially Mecca, there is a lack of epigraphic evidence, but details are found in the writings of Muslim authors of the Abbasid era.^[4] Some historians maintain that the pre-Islamic calendar used in Central Arabia was a purely lunar calendar similar to the modern Islamic calendar.^[5][4][6] Others concur that the pre-Islamic calendar was originally a lunar calendar, but suggest that about 200 years before the Hijra it was transformed into a lunisolar calendar, which had an intercalary month added from time to time to keep the pilgrimage within the season of the year when merchandise was most abundant.^[7][8] Safaitic evidence (discussed below) strongly suggests that it was not a Lunar calendar, however this evidence needs yet to be fully taken into account by current scholarship.

In Safaitic inscriptions, both seasons and Zodiac signs are used to refer to specific times. Four different Safaitic seasons are documented: 'winter' s²ty, which corresponds to early January-mid-February, 'the season of the later rains' dṯʔ, taking place in mid-February till mid-April, 'the early summer' ṣyf, lasting from mid-April till early June and finally the 'dry season' qyẓ, lasting from early June till early October. Rwala bedouins also have a similar system, although it is more complete, and includes aṣ-ṣferi, the fifth season, early October-early January, which is lacking from Safaitic attestations. Besides, they call dṯʔ as-smāk, which is from a different root.^[9] These Safaitic seasons can be seen in, for instance, Mu 113

l s ʿd bn ḍb bn ʿbd bn ʾdm w ḥll h- dr dṯʾ f ʾyḍ f s²ty f h bʿls1mn qbll

"By Ṣʿd son of Ḍb son of ʿbd son of ʾdm and he camped here during the season of the later rains, then the dry season, and then winter so, O Bʿls¹mn, show benevolence" (Baʕl-Samān was the name of a Safaitic god).^[10]

These seasons were connected to Zodiac signs which, in any case, had a very important place in the pre-Islamic calendars, whether South Arabian or Safaitic. In many places these Zodiac signs are used to refer to specific past events.^[11] Below are cited the names of the pre-Islamic Safaitic Zodiac names (ḏ corresponds to voiced English th in the and ṯ to unvoiced English th in throngs), the list of which is incomplete as the word for Cancer is insecure):

As in some Safaitic texts, series of Zodiac signs correspond to (in other texts) the same series of months, denoting the same seasons of the year,^[12] it is obvious that the Arabian nomads from the desert did not use a 360-days calendar without intercalation, nor a purely lunar calendar, as otherwise Zodiac signs would not match the months and seasons. The mention of dṯʔ qyẓ s²ty in Safaitic inscriptions, being a description of the whole year, corresponding to the often re-occurring phrase mlḥ w ḏkr w ʔmt "Aquarius and Aries and Libra", shows that the nomadic year started with the season of rains following the winter, namely dṯʔ (mid-February to mid-April), exactly like the South Arabian year.^[13] However, as Al-Jallad (2016: 86) argues, we would then expect the equivalent Zodiacal sequence to start with Aries, and not with Aquarius as it does (mlḥ w ḏkr w ʔmt). This is because the Safaitic Zodiac did not correspond to our notion of the Zodiac, but each sign started when the Sun entered the constellation, and in no way it is connected to a Lunar calendar where the Zodiac names simply could be equated to their corresponding month names.

Sources for the names of these pre-Islamic months are al-Muntakhab min Gharīb Kalām al-ʿArab^[14] by Ḥasan of Abū al-Ḥasan ʿAlīy bin al-Ḥasan bin al-Ḥusayn al-Hunāʾī ad-Dūsā (d. 309 A.H./921 C.E.), better known as "Kurāʿ an-Naml", and Lisān al-ʿArab^[15] of Ibn Manẓūr (d. 711 A.H./1311 C.E.). Al-Biruni and al-Mas'udi suggest that the Ancient Arabs used the same month names as the Muslims, though they also record other month names used by the pre-Islamic Arabs.^[4]

Unlike the common Arabic usage of equating rabīʿ to the spring (so is its meaning in all modern Arabic dialects), Classical lexicographers translate it as 'autumn' and equate it to xarīf 'autumn'.^[16] We have thus the possibility to deduce the general position with the year of the following months, based on the assumption that rabīʿ al-ʾawwal designates, as its name indicates, early autumn.

Some suggested that the Arab pilgrimage festivals in the seventh and twelfth months were originally equinoctial festivals^[17] and research on the pre-Islamic calendar has been summarized in recent Islamic^[18] and secular^[19] scholarship which equates the pre-Islamic months from Muharram to Dhu al-Hijjah with the Hebrew religious months of Iyyar (second) to Nisan (first) respectively (Ramadan corresponding to the Fast of Adam in Tevet) rather than Nisan (first) to Adar (twelfth) as might otherwise be presumed. In stark opposition to this opinion however, subsequent Christian^[20] then Jewish^[21] scholars have both tried to equate the pre-Islamic months from Muharram to Jumādā ath-Thāniya at least with the Hebrew months of Tishrei to Adar I respectively. Nevertheless, the Islamic position equating Nisan with Dhū al-Ḥijja has prevailed.^[19] Nisan is the month of spring in the Hebrew calendar and Babylonian calendar, which are both lunisolar calendars with either 12 or 13 months.

The Islamic tradition is unanimous in stating that Arabs of Tihamah, Hejaz, and Najd distinguished between two types of months, permitted (ḥalāl) and forbidden (ḥarām) months.^[4] The forbidden months were four months during which fighting is forbidden, listed as Rajab and the three months around the pilgrimage season, Dhu al-Qa‘dah, Dhu al-Hijjah, and Muharram.^[4] A similar if not identical concept to the forbidden months is also attested by Procopius, where he describes an armistice that the Eastern Arabs of the Lakhmid ruler, al-Mundhir II, respected for two months in the summer solstice of 541 AD/CE.^[4] However, Muslim historians do not link these months to a particular season.^[4]

The Qur'an links the four forbidden months with Nasi' (Arabic: ٱلنَّسِيء, an-nasīʾ), a word that literally means "postponement".^[4] According to Muslim tradition, the decision of postponement was administered by the tribe of Kinanah,^[6] by a man known as the al-Qalammas of Kinanah and his descendants (pl. qalāmisa).^[22]

Different interpretations of the concept of Nasī’ have been proposed.^[23] Some scholars, both Muslim^[24][25] and Western,^[4][6] maintain that the pre-Islamic calendar used in Central Arabia was a purely lunar calendar similar to the modern Islamic calendar. According to this view, Nasī’ is related to the pre-Islamic practices of the Meccan Arabs, where they would alter the distribution of the forbidden months within a given year without implying a calendar manipulation. This interpretation is supported by Arab historians and lexicographers, like Ibn Hisham, Ibn Manzur, and the corpus of Qur'anic exegesis.^[26]

This is corroborated by an early Sabaic inscription, where a religious ritual was "postponed" (ns'’w) due to war. According to the context of this inscription, the verb ns'’ has nothing to do with intercalation, but only with moving religious events within the calendar itself. The similarity between the religious concept of this ancient inscription and the Qur'an suggests that non-calendaring postponement is also the Qur'anic meaning of Nasī’.^[4] Thus the Encyclopaedia of Islam concludes "The Arabic system of [Nasī’] can only have been intended to move the Hajj and the fairs associated with it in the vicinity of Mecca to a suitable season of the year. It was not intended to establish a fixed calendar to be generally observed."^[27]

Others concur that it was originally a lunar calendar, but suggest that about 200 years before the Hijra it was transformed into a lunisolar calendar containing an intercalary month added from time to time to keep the pilgrimage within the season of the year when merchandise was most abundant. This interpretation was first proposed by the medieval Muslim astrologer and astronomer Abu Ma'shar al-Balkhi, and later by al-Biruni,^[22][28] al-Mas'udi, and some Western scholars.^[29] This interpretation considers Nasī’ to be a synonym to the Arabic word for "intercalation" (kabīsa). The Arabs, according to one explanation mentioned by Abu Ma'shar, learned of this type of intercalation from the Jews.^[6][22][28] The Jewish Nasi was the official who decided when to intercalate the Jewish calendar.^[30] Some sources say that the Arabs followed the Jewish practice and intercalated seven months over nineteen years, or else that they intercalated nine months over 24 years; there is, however, no consensus among scholars on this issue.^[31] The metonic cycle of 19 years was established for intercalating the Hebrew calendar since the time of their exile in Babylonian, and it was also observed in the Babylonian calendar as well, starting in the same period. The Kinānah tribe, during the time of Muhammad, was in charge of authorizing the intercalation; that the Kinānah tribe had taken over this task from the Kinda tribe, which had been Judaized for hundreds of years previously, lends credence to the position that the process of intercalation may have been borrowed from the Jewish tradition.^[32] Referring to Abū Rayḥān al-Bīrūnī (d. ca. 442 A.H./1050 C.E.), it has been posited that this intercalation was effected in order to accommodate the scheduling of seasonal trade cycles with annual pilgrimages,^[33]

The prohibition of nasi' in AH 10 has been suggested as having had the purpose of wresting power from the Kinānah clan who was in control of intercalation, but there is no consensus regarding this position.^{[citation needed]}

The names for the days of the week in pre-Islamic Arabia were changed during the era of Islam to numbers ("the first (day)", "the second (day)", etc.) with the exception of the sixth day, "Friday", whose name means "congregation", in reference to this being the Islamic day of communal prayer. The numbering follows the account of the creation in six days, with the seventh the day of rest, in the creation narrative in the Book of Genesis. Prior to this, the pre-Islamic Arabian days of the week were:

• Islamic calendar
• Solar Hijri calendar
• Assyrian calendar
• Persian calendar
• Rumi calendar
• Arabic names of Gregorian months

• Al-Jallad, Ahmad (2014). "An Ancient Arabian zodiac. The constellations in the Safaitic inscriptions, Part I." Arabian archaeology and epigraphy 25: 214-230.
• Al-Jallad, Ahmad (2016). "An ancient Arabian zodiac. The constellations in the Safaitic inscriptions, Part II" Arabian archaeology and epigraphy 27: 84-106.
• Varisco, D.M. 1987. "The Rain Periods in Pre-Islamic Arabia" Arabica 34/2: 251–266.
• Varisco, D.M. 1991. "The Origin of the Anwa’ in Arab Tradition" Studia Islamica 74: 5–28.