  Pure Yang-Mills instantons are considered on S^1 x R^3 -- so-called calorons.
The holonomy -- or Polyakov loop around the thermal S^1 at spatial infinity --
is assumed to be a non-centre element of the gauge group SU(n) as most
appropriate for QCD applications in the confined phase. It is shown that a
charge k caloron can be seen as a collection of nk massive magnetic monopoles
each carrying fractional topological charge. This interpretation offers a
physically appealing way of introducing monopole degrees of freedom into pure
gluodynamics: as constituents of finite temperature instantons. New and exact
solutions are found along with the fermionic zero-modes of the Dirac operator.
The properties of the zero-modes are analysed as well as the hyperkahler and
twistor geometry of the caloron moduli space. Lattice gauge theoretic
applications are also mentioned.
