C =
, another form of θ, and confounded with C as though standing for centum.
M = φ, becoming first CI
and then M, as though standing for mille, D is one half of this figure, or I
[3].
[1]. Quintilian, I. 7, 14. When i is doubled it always denotes the consonantal i (j); e.g. maiior.
[2]. Cf. Ball's History of Mathematics, pp. 119, 120.