4 unit min rule

Just wondering if anyone knows if you have to build all military units as 4 minimum or if special units (like dragons) are still individual?  A 4 dragon unit would be scary but would take far too long to make, cost $4000 and only have 2 attacks.  4 individual dragons would be much more fun.  Or are dragons gone?  I haven't been able to play far enough with the restricted prestige and research/building costs to investigate this yet.

Cheers, CP.