Ever since Emperor
Constantine I () introduced it in 309, the Byzantine Empire's main coinage had been the high-quality
solidus or
nomisma, which had remained standard in weight (4.45
grams) and
gold content (24
carats) through the centuries. Emperor
Nikephoros II Phokas (), however, introduced a new coin, the
[nomisma] tetarteron ("quarter [coin]") which was 2 carats (i.e. about 1⁄12, despite its name) lighter than the original
nomisma. The latter now became known as the
histamenon, from the Greek verb , "to stand up", implying that these followed the traditional standard. The reasons for this change are not clear; Byzantine chroniclers, however, suggest fiscal motives, reporting that Nikephoros collected the taxes as before in the
histamenon while paying back with the
tetarteron, which was officially rated as equal in value to the full-weight coin. (r. 1057–1059), with its by then characteristic concave form Initially, the two coins were virtually indistinguishable except in weight. During the later reign of
Basil II (), the
tetarteron began to be minted in a thicker and smaller form, while the
histamenon became correspondingly thinner and wider. Only during the sole rule of
Constantine VIII () did the two coins become iconographically distinct as well. By the mid-11th century, the
tetarteron measured 18 mm wide and its weight apparently standardized at 3.98
grams, i.e. three carats less than the
histamenon or
stamenon (a name first attested in 1030), which now measured 25 mm in diameter (as opposed to 20 mm for the original
solidus). In addition, under
Michael IV the Paphlagonian (), it began to be minted in a slightly concave (scyphate) form, possibly to increase the thin coin's strength and to make it less easily bent. Flat coins were still struck at times, but scyphate ones came to predominate from
Constantine IX () on and became standard under
Isaac I Komnenos (). These concave coins were known as
histamena trachea or simply
trachea (τραχέα, "rough, uneven") from their shape. ==Debasement and abolition==