No fireplace has less than two, one firedog on either side for supporting logs or grate.
But today, possibly because the name sounds more highfalutin, we speak of them as andirons.
Formerly, however, the dogs, as they were then called, were of utilitarian iron, serving as supports, and the andirons, in households that afforded them, were state affairs of highly polished brass.
Why dog?
Because they were low, serviceable, and stood (usually) on four legs.
