Aurelian was born on 9 September, most likely in 214 AD, although 215 AD is also possible. The ancient sources do not agree on his place of birth, although he was generally accepted as being a native of Illyricum but, another common belief was that he was born in Greece. According to the author of the Historia Augusta, "Aurelian was born of a humble family, at Sirmium according to most writers, but in Dacia Ripensis according to some. I remember, moreover, having read one author who declared that he was born in Moesia". The province of Dacia Ripensis was actually created in Moesia by Aurelian as Emperor when he abandoned the old trans-Danubian territory of Dacia. The Roman historian Eutropius also opts for the area that later became Dacia ripensis. The academic consensus is that he was of humble birth and that his father was a peasant-farmer who took his Roman nomen from his landlord, a senator of the clan Aurelius. Saunders suggests that his family might in fact have been of Roman settler origin and of much higher social status; however, his suggestion has not been taken up by his more recent academic colleagues such as Southern and Watson.
Using the evidence of the ancient sources, it was at one time suggested that Aurelian's mother was a freedwoman of a member of the clan Aurelius and that she herself was a priestess of the Sun-God in her native village. These two propositions, together with the tradition that the clan Aurelius had been entrusted with the maintenance of that deity's cult in Rome, inspired the notion that this could explain the devotion to the sun-god that Aurelian was to manifest as Emperor - see below. However, it seems that this pleasant extrapolation of dubious facts is now generally accepted as being no more than just that.