Anonymous AR Third-Siliqua, AD 580-600. 15 mm, 0.67 g. 

Helmeted, draped, and cuirassed bust of Constantinopolis right.
Large TX monogram.

Bendall 12; BMC 1981-1-28-1. 

With permission of Pecunem & Gitbud & Naumann - Auction 21, Sept. 2014.
Estimate 50 Euros.