Medieval Cyrillic manuscripts and Church Slavonic printed books have two variant forms of the letter Zemlja: з and ꙁ.

Only the form ꙁ was used in the oldest ustav (uncial) writing style; з appeared in the later poluustav (half-uncial) manuscripts and typescripts, where the two variants are found at proportions of about 1:1.

[1] Some early grammars tried to give a phonetic distinction to these forms (like palatalized vs. nonpalatalized sound), but the system had no further development.

Ukrainian scribes and typographers began to regularly use З/з in an initial position, and ꙁ otherwise (a system in use till the end of the 19th century).

Russian scribes and typographers largely abandoned the widespread use of the variant ꙁ in favor of з in the wake of Patriarch Nikon's reforms.