Adverb
On this; hereon.
Source: Webster's dictionaryHereupon Juno and Pallas leap sheer down from the sky upon the rocks; this one the daughter of Jove, that one his spouse constrains. Gaius Valerius Flaccus
Venomous animals, when they bite or sting, inflict a wound, and instil into it a drop or more of liquor, which infects the fluid of the nerves, and by this means inflames the membranes: hereupon a swelling arises, sometimes to a degree of mortification, which spreads to the neighbouring parts. Richard Mead
hereupon, the passengers stumbled aboard Source: Internet