Centered at the ancient city of Petra located in what is now the modern kingdom of Jordan, the Nabataeans built a kingdom in the 2nd century BCE that grew prosperous from trade routes that crisscrossed their territory. At its height the Nabataean kingdom extended from Syria to the Hijaz in Saudi Arabia, and from Jordan into the Sinai in Egypt. The wealth and the strategic location of the Nabataeans eventually piqued the Romans' interest, and it led to their conquest in 106 CE and incorporation into the Roman Empire as the province of Arabia Petraea.
In the first millenium BCE, Aramaic was the international language and script of trade, and the Nabataeans adopted both as their written language. However, personal names on monumental inscriptions reveal that they were in fact Arabs. It is actually not uncommon for a people to speak one language and write another, as the written language often holds such prestige that the learned class will only write in it.
Gradually, the Nabataean's variant of the Aramaic script evolved from the angular shape of the original to a more cursive style with ample use of ligatures to join the letters of words together. Despite living under Roman rule, the Nabataeans continued to write with their script well into the 4th century CE, at which time the language behind the script shifted from Aramaic to Arabic. Nabataean is therefore considered the direct precursor of the Arabic script. In fact, one of the earliest inscriptions in the Arabic language was written in the Nabataean alphabet, found in Namarah (modern Syria) and dated to 328 CE. This date is considered by many scholars to be the date that Nabataean script "became" the Arabic script, although in reality the transition from one to the other occurs gradually over centuries.
The following chart illustrates and compares the Aramaic, Nabataean, and Arabic alphabets.