Answer: TRIPLE DECAPITATION
The inscriptions on the nine tombstones reference real-world heads of state, with some details changes to make them sound Atlantean. The inscriptions are ordered alphabetically by real-world name.
Count Aquarius I | Abraham Lincoln |
Blue Fin | Alaric I |
Prince Anchovy II | Augusto Pinochet |
Metis Quartz | Catherine II |
Blue Stream | Cuitláhuac |
Pontus of Styx | Edmund Barton |
Sir Dolphin | Edward VIII |
Eel the Brave | Genghis Khan |
Old Nereus | Hammurabi |
Poseidon the Wise | Harald Bluetooth |
Pacific X | Louis XIV |
Whirl the King Exiler | Lucius Junius Brutus |
Lord Neptune the Superior | Nebhepetre Mentuhotep II |
Poseidon XXV | Pharnaces II |
Pacific V | Philip II |
Ox the Patriarch | Robert the Bruce |
Moonrise I | Shinzo Abe |
Nemertia | Wu Zetian |
Each real world name is the same length as the corresponding fake name. For each pair of real and fake names, there is exactly one index at which they have the same letter. Ordering these letters chronologically by real-world head of state gives the answer.
NEBHEPETREMENTUHOTEPII LORDNEPTUNETHESUPERIOR HAMMURABI OLDNEREUS LUCIUSJUNIUSBRUTUS WHIRLTHEKINGEXILER PHARNACESII POSEIDONXXV ALARICI BLUEFIN WUZETIAN NEMERTIA HARALDBLUETOOTH POSEIDONTHEWISE GENGHISKHAN EELTHEBRAVE Erratum: there is also an overlapping H. ROBERTTHEBRUCE OXTHEPATRIARCH CUITLAHUAC BLUESTREAM PHILIPII PACIFICV LOUISXIV PACIFICX CATHERINEII METISQUARTZ ABRAHAMLINCOLN COUNTAQUARIUSI EDMUNDBARTON PONTUSOFSTYX EDWARDVIII SIRDOLPHIN AUGUSTOPINOCHET PRINCEANCHOVYII SHINZOABE MOONRISEI
These letters spell the answer, TRIPLE DECAPITATION.