How should I understand the meaning of 'start' in this sentence in Virginia Woolf's Orlando?

I’m reading Virginia Woolf’s Orlando, however in the first paragraph in Chaptet 1 I ran into this sentence

Orlando’s father, or perhaps his grandfather, had struck it from the shoulders of a vast Pagan who had started up under the moon in the barbarian fields of Africa.

See, I went to all the dicts (all the ones I can find) to see whether there is such a phrasal verb as ‘start up’ or not, but surely ‘start up sth such as business’ isn’t logically comprehensible considering the context.

I am now wondering if this ‘start’ means ‘a slight movement of body because you’ve been surprised or excited’.

Thank you for your help.