  We define a period map for classical Campedelli surfaces, using a covering
trick as in the case of Enriques surfaces: the period map is shown to come from
a family of Enriques surfaces, obtained as quotients of the Campedelli surface
by an involution.
  The period map realises an isomorphism between a projective variety obtained
by invariant theory, and the Baily-Borel compactification of an arithmetic
quotient, in the same fashion as in the work of Matsumoto, Sasaki and Yoshida.
The result is proved from scratch using traditional methods.
  As another consequence we determine properties of the monodromy of Campedelli
surfaces with a choice of double cover.
