looked up the list of the levels. it does seem short.
The Shores of Attica TSOA111
BOSS: Basilisk BAS222
BOSS: Persian King PERKING333
BOSS: Basilisk Round 2 BASR2444
The City of Marathon TCOM555
The Temple of Helios TTOH666
The Caves of Olympus TCOO777
The Temple of Helios Part 2 TTOHP2888
The River Styx TRS999
BOSS: Charon CHAR1010
The Depths of Tartarus TDOT1111
BOSS: Charon Round 2 CHAR21212
The Temple of Persephone TTOP1313
Fields of Elysium FOE1414
BOSS: Persephone PER1515