The earliest Bantu-speaking communities entered eastern Africa during the last five centuries B.C.E. Swahili is a member of the Bantu subgroup known as Sabaki. Proto-Sabaki was likely spoken on or near the East African coast during the first half of the first millennium C.E., and Proto-Swahili on the coast a century or two later. Based on archeological and linguistic data, the earliest Swahili settlements along the coast from southern Somalia to Mozambique are usually assigned to 800 C.E. or slightly earlier. A set of 1,400 lexical reconstructions for Proto-Sabaki and thus Proto-Swahili (Nurse and Hinnebusch, chap. 3 and apps.) show that few were necessarily derived from Persian (or Arabic) during most of the first millennium C.E.; that is, either the items are also attested in Arabic and/or Indic languages in an identical or similar form, which means these languages could also be the source, or they are not cognate across the Swahili dialect spectrum, which means that, although we tentatively reconstructed them from the early protostage, they more likely entered Swahili later. The paucity of lexical material at this stage as well as the total absence of nonlexical material suggest very light Persian influence. The few items of general reference at this stage include *(m)pula “steel,” *bwana “man, gentleman,” *(m)pamba “cotton,” and *(n)kasa “turtle,” which correlate with Middle Persian pōlāwad, bān, pambag, and kašawag.

By about 1700, when the first recorded documents in Swahili appeared, Swahili vocabulary was much as it is today, containing several hundred items from Persian (Krumm; Knappert) and many more from Arabic. Thus, most of these entered Swahili between 800 and 1700. The recentness of their arrival is corroborated by their having undergone only recent and local sound shifts affecting Swahili. They cluster in certain categories—tools, ornaments, spices, plants, household items, and maritime and kinship terms—and contain few general items. This pattern derives from trading contact rather than sustained political intertwining. As with the small, earlier set, it is possible that many entered Swahili indirectly via Arabic or Indic languages. Many are also attested in Comorian and Mwani, a Swahili-like language on the Mozambique coast.