Serrhēum — Lewis & Short
Serrhēum (-rhīum, -rīum), i, n.,
I a promontory in Thrace, with a fortification:
alia castella, Cypsela et Doriscon et Serrheum,Liv. 31, 16, 5; Mel. 2, 2, 8.—
Form Serrium,Plin. 4, 11, 18, § 43.