In the south, much of coastal Thrace had passed under the rule of Athens, making them direct neighbours of the Odrysians. The Athenians had already taken some interest in the Thracian interior before 431, but it was in said year when they concluded an alliance with Sitalces against Perdiccas II of Macedon in the west. This pact was cemented by a dynastic marriage, as Sitalces would marry the sister of the Athenian ambassador, Nymphodoros of Abdera. Sitalces' son Sadokos was sent to Athens and was granted the Athenian citizenship. Sitalces, apparently an experienced leader with political acumen, would prove his commitment to the alliance in the next year, when he arrested a Peloponnesian embassy that tried to persuade him to join the Spartan side and handed it over to Athens.