In the late 10th century, the theme was divided in two parts: Strymon proper, also known as Chryseuba or Chrysaba (Χρυσεύβα/Χρυσάβα, according to the Greek scholar Nikolaos Oikonomides a Hellenized form of "Krushevo", modern Achladochori), and the theme of New Strymon (Νέος Στρυμών). The latter is known only through the "Escorial Taktikon" of c. 975. Oikonomides identifies it either with the portion of the old theme east of the Nestos, which was later raised to a separate theme as Boleron (Greek: Βολερόν), or with a northern portion along the upper Strymon, possibly acquired after Emperor John I Tzimiskes's (r. 969–976) conquest of Bulgaria in 971. Towards the end of the 10th century, the theme of Strymon appears to have been united with that of Thessalonica and perhaps also Drougoubiteia, while in the 11th century it appears united with Boleron.