Last Seen in Massilia is a historical novel by American author Steven Saylor, first published by St. Martin's Press in 2000.
It is the eighth book in his Roma Sub Rosa series of mystery stories set in the final decades of the Roman Republic.
Lost in the woods, the pair stumble upon a small temple where they run into two of Caesar's soldiers and an alleged soothsayer who urges Gordianus to turn back instead of seeking his son.
Following the soldiers to Caesar's camp, Gordianus meets Gauis Trebonius, the officer in charge of the siege of Massilia.
Before they can come to a consensus, they are interrupted by a group of armed men led by Apollonides, the First Timouchos and the de facto leader of Massilia.
Blearily, Gordianus spends the following days wallowing in grief until a Gaul merchant named Arausio calls upon him.
He reveals that his daughter was the one who they saw fall from the rock and that she suffered from heartbreak by Zeno, Apollonides' son-in-law, who married the deformed Cydimache.
While there, the corrupt former governor shows Gordianus and Davus his secret treasure room housing the eagle standard of Gaius Marius, last seen with Catilina.
Disappointed by the trio, Gordianus and Davus head back to Hieronymus' house but realize they are being followed.
Early the next day, a messenger ship sneaks past Caesar's blockade to Massilia, spreading word that Pompey was sending reinforcements.
After watching eighteen Massilian vessels sail out to meet with Pompey's reinforcements, the trio are surprised to see one return not too long after.
Badly damaged, no other ships follow but Davus is able to spy the so-called relief fleet—sailing west for Spain.
While heading back towards Apollonides' house, they notice a giant sinkhole on the spot they first emerged, causing a breach in the walls.
Back at Apollonides' house, Arausio and his wife await in front of Zeno and Cyndimache's quarters.
Trying to ingratiate himself into Apollonides' household, Meto agrees to masquerade as Cyndimache while Zeno hopes to get into Caesar's good graces.
Near the end of their conversation, Zeno reveals that Cyndimache was pregnant with his child which was why he tried to save her at first but upon seeing her face again, pushed her instead.
Angry that Meto didn't contact him, Gordianus almost loses his temper only to be interrupted by Caesar's men breaching the walls.
Gordianus then spots a procession making its way towards Caesar, led by Meto carrying the eagle standard of Marius.
Upon reaching the rock, Hieronymus switched clothes with an unwilling Zeno who was then pushed over the edge along with his father-in-law.