70. #x# is a compound consonant, standing for #cs#, and so sounded,
never as English _gs_ or _gz_.
71. _z_, being a Greek sound, should have retained its Greek
pronunciation. This differed in the different dialects; in the Attic of
the fourth century B.C. it was approximately that of English _z_ in
_zeal_, while its earlier value was _zd_. The Romans had great
difficulty in pronouncing this sound (Quint. 12, 10, 27 f.), but the
grammarian Velius Longus expressly states that it should not be
pronounced as a compound sound (_zd_).
72. About 100 B.C. the combinations #ch#, #ph#, and #th# were introduced
in Greek words to represent χ, φ, and θ; as #Philippus#, for the older
PILIPVS. Somewhat later these combinations were in general use in some
Latin words (19). #ch# is thought to have been pronounced like _kh_ in
_blockhead_, #ph# as in _uphill_, and #th# as in _hothouse_. But in
practice #ch# is usually sounded as in the German _machen_ or _ich_,
#ph# as in _graphic_, and #th# as in _pathos_.