A sacrifice of a hundred oxen or cattle at the same time; hence, the sacrifice or slaughter of any large number of victims.

the sacrifice of a hundred cattle

100 oxen or cattle (in ancient Greece a public sacrifice of 100 oxen to the gods in thanks for some great discovery, event or victory)

a great sacrifice; an ancient Greek or Roman sacrifice of 100 oxen

(noun) Originally, a blood sacrifice to Greek or Roman gods consisting of exactly one hundred oxen or cattle; later, any large-scale sacrifice or slaughter for religious purposes [Latin hecatombe, Greek hekatombe

In Ancient Greece, a Hecatomb (Ancient Greek / hekatómbê) was the sacrifice to the gods of 100 cattle (hecaton = one hundred).