Philippi can be found on Google Earth here.
The First Battle took place on the 3rd of October, the Second Battle on the 23rd - and it was a decisive victory for Octavian and Mark Anthony against Cassius and Brutus, the assassins of Julius Caesar. Cassius committed suicide after the first Battle, Brutus after the second.
Many dates are claimed by historians to mark the 'real' end of the Republic, and this is one of them - although the Republic limped on in theory, after the battle Rome was divided between and rule by Anthony and Augustus.
The third member of the Second Triumvirate was Marcus Aemilius Lepidus. His maternal grand-father was Lucius Appuleius Saturninus, who was murdered in 100 BC, whilst Tribune for the second time.
Marcus Livius Drusus Claudianus also killed himself after the battle - he was the son of the Drusus who was murdered when Tribune in 91 BC, and the father of Livia. His family had to flee Rome because of Augustus' proscriptions, which makes it all the more ironic that Livia became Augustus' third wife.
I'm making the points about family connections because of something in modern scholarship I've been having a huge problem with - too many historians assume that just because people knew each other, or were related, that they were on the same 'side' politically. This may be truer later, but for Marius' day it need not have been and is a huge assumption to make.
Saturninus and Drusus are both described as allies of Marius in some modern histories, pushing through his political agenda. There is no evidence of any support by Marius for Drusus and his reforms. There is some evidence for Saturninus allying himself with Marius - though in the end Marius helped remove the Tribune from office. Julius Caesar was Marius' nephew and sometimes claimed to be his political heir; Anthony and Augustus claimed to be the heirs of Caesar.
But as we can see in the tangled links between Livius Drusus Tribune of 91, his son, and his son's daughter ... one can read too much into briefs mentions in the sources; if we did not know Livia's father had killed himself, and that her family had fled because of Octavian's proscriptions, and we only knew they had later married ... some historians might have tried to posit that Octavian and her father were allies in 42. Basically that's the sort of modern history I've been reading for Marius' period, much of it built on a house of cards.