The Arabic script is not an invention but an inheritance, and its line of descent is agreed in outline. The Phoenician alphabet gave rise to Aramaic; Aramaic was used by the Nabataeans, the trading kingdom centred on Petra whose territory ran across northern Arabia and the southern Levant; and the cursive form of Nabataean writing, as it appears in inscriptions and on papyri from the first centuries of the common era, is the immediate ancestor of Arabic writing.
Two features of Arabic follow directly from that ancestry. The first is the joining of letters, which the Nabataean cursive had already begun and which Arabic completed and regularised, including the group of letters that connect on one side only. The second is the shortage of shapes. Aramaic had twenty-two letters; the cursive merged several of them into one outline; and Arabic needed to write twenty-eight consonants with what remained. The dots that distinguish ba from ta and jim from ha are the repair for that shortfall.
A small number of pre-Islamic inscriptions in the Arabic language written in a script transitional between Nabataean and Arabic are the physical evidence for the transition, and they are dated to the fourth, fifth and sixth centuries of the common era. The atlas records the outline and the date range rather than a single origin point, because the corpus is small, several individual inscriptions are read differently by different epigraphers, and new finds have repeatedly moved the argument. What is settled is the family: Arabic writing is a branch of Aramaic writing, and its nearest relatives are Nabataean, Syriac and the square Hebrew script, all of which reached their present forms from the same stock.