Wikipedia
In Greek mythology, the Pallantidai were the fifty sons of Pallas, nobles of Attica, and rivals of their uncle Aegeus and his son Theseus over the Athenian throne. Diodorus Siculus related that they once became friends with Androgeos, a son of Minos, and that was why Aegeus had Androgeos assassinated, fearing that Pallas and his sons could use this friendship to get assistance from the powerful Minos against him. After Aegeus' death the Pallantidae and their father marched against Theseus because they would not accept him as king and hoped to gain control over Athens. According to Plutarch, one half of them under command of Pallas openly marched from Sphettus, while the other half laid an ambush near Gargettus. Their plan failed though, because Leos, their herald, warned Theseus of their schemes and an ambush they had prepared for him. Theseus pre-emptively ambushed the Pallantides and killed all those at Gargettus, whereupon the other half retreated. Other sources state that Theseus killed all the fifty Pallantidae as well as Pallas. A tradition saying that he spared their sister, Aricia, whom he kept as slave, is followed in Jean Racine's Phèdre but is not supported by extant genuinely ancient sources.
Ovid mentioned two of the Pallantidae, the young Butes and Clytus, as companions of Cephalus. Other than this, no individual names of any of the Pallantidae survived.
Some scholars believe that the east frieze of the Hephaisteion depicts the battle of Theseus against the Pallantidae.