16 Roman Soldiers March In                                                                                            4 March Out

soldier               arrow                                

                                                                                                                    dead soldier ldead soldier ldead soldier ldead soldier ldead soldier ldead soldier ldead soldier l

dead soldier rdead soldier rdead soldier rdead soldier r  (12 died)

Cohort of 16 go through battle from time 0 to time 1.  12 die, 4 survive.  Mortality rate = 12/16/battle