  Alkaline earth mono-silicides ({\AE}Si, {\AE} $=$ Ca, Sr, Ba) are poor metals
and their transport properties are not solely determined by the Zintl anion, in
contrast to their Zintl-type composition. Their conducting network is formed by
the depopulated ${}^{1}_{\infty}$[Si$^{2-}$] $\pi$-system and {\AE}-$d$ states.
This justifies the special local coordination of the metal atoms and the
planarity of the silicon chains. The low density of carriers seems to be a
playground for magnetic instabilities and the triangular prismatic arrangement
of {\AE} atoms responsible for the observed weak glassy behavior.
