Scientific studies of Pre-Islamic Arabs starts with the Arabists of the early 19th century when they managed to decipher epigraphic Old South Arabian (10th century BCE), Ancient North Arabian (6th century BCE) and other writings of pre-Islamic Arabia. Thus, studies are no longer limited to the written traditions, which are not local due to the lack of surviving Arab historians' accounts of that era; the paucity of material is compensated for by written sources from other cultures (such as Egyptians, Greeks, Romans, etc.), so it was not known in great detail. From the 3rd century CE, Arabian history becomes more tangible with the rise of the Ḥimyarite, and with the appearance of the Qaḥṭānites in the Levant and the gradual assimilation of the Nabataeans by the Qaḥṭānites in the early centuries CE, a pattern of expansion exceeded in the Muslim conquests of the 7th century. Sources of history include archaeological evidence, foreign accounts and oral traditions later recorded by Islamic scholars—especially in the pre-Islamic poems—and the Ḥadīth, plus a number of ancient Arab documents that survived into medieval times when portions of them were cited or recorded. Archaeological exploration in the Arabian Peninsula has been sparse but fruitful; and many ancient sites have been identified by modern excavations. The most recent detailed study of pre-Islamic Arabia is Arabs and Empires Before Islam, published by Oxford University Press in 2015. This book collects a diverse range of ancient texts and inscriptions for the history especially of the northern region during this time period.