From Longman Dictionary of Contemporary Englishhappen on/upon somebody/something phrasal verb literary or old-fashionedFINDto find something or meet someone by chance SYN come across I happened on the restaurant by chance. → happen→ See Verb table
Examples from the Corpus
happen on/upon • The landing is supposed to have happened on December 27,1980.• How often do events of this sort, which leave no enduring geological record, happen on Earth?• The accident happened on Interstate 84 in Manchester, about 10 miles east of Hartford, during evening rush hour.• And what would happen on nanny's nights off?• There's nothing that happens on the estate which I don't know about.• That happened on the first and second of the month.• I want to travel around and talk to people about what is happening on the ground.• When I explained what had happened on the train he shook his head and said one should never trust the Moors. 