'Novel' is a disputed term - the popular consensus is that 'novels' are a modern invention, but this does not take into account ancient sources like Petronius' 'Satyricon' (1st century CE).

Whether this source is a 'novel', especially since the Satyricon only survives in fragments (much of it is lost), is disputable, but academics frequently describe it as such.

Source and further reading:

E. Young (undergraduate essay), 'Can the Satyricon be described as a Realistic Novel?'

V. Rimmel (2005), 'The satiric maze: Petronius, satire, and the novel' in K. Freudenberg (ed) 'The Cambridge Companion to Roman Satire', pages 160-173.