"Except they meant to bathe in reeking wounds / Or memorise another Golgotha" (1:2)
A reference to Christ's death at Golgotha/upon Mount Cavalry, known proverbially as 'the place of dead men's skulls'.
Golgotha is an Aramaic word meaning 'skull' and Cavalry is from the Latin work 'calva' meaning 'blad head' or 'skull'.
The actual site of Christ's crucifixion is unclear, with many believing it took place on a steep rocky ridge outside the walls of Jerusalem. The ridge contained two large sunken holes, resembling the face of a skull.
A bleeding sergeant tells King Duncan of Macbeth's blood exploits on the field of battle; his actions were so bloody, that the captain wonders whether Macbeth and Banquo were trying to replicate the scenes at Christ's crucifixion.
It could also be suggested that just as Christ was killed by soldiers, Duncan will potentially suffer the same fate.