Why were so many praenomina ordinal numbers or apparently derived from ordinal numbers?
A few examples:
- Octavia Minor (Augustus Caesar's older sister)
- Octavia Major (Augustus Caesar's older half-sister)
- Quintus Aelius Paetus
- Sextus Aelius Paetus (the latter's son)
- Quintus Mucius Scaevola (pontifex maximus, 89–82 B.C.)
- Mucia Tertia (his daughter, maybe not a praenomen)
- Sextus Empiricus
- Septimius Severus
I'm pretty sure that the Romans were not simply numbering their children in the order they were born, since a first child might indeed be named Sexta or any other number—but not Quarta or Quartus, since those were never used as praenomina. According to this Wikipedia article, in the Julii Caesares, if you were male, you could only be named Gaius, Lucius, or Sextus.
If the Romans themselves weren't sure, did they ever at least ask themselves, "Isn't it strange that we're naming our children after numbers?"