Anyone with a counting board also has zeros, as empty places with no counters, and ancient people had no problem understanding and using the concept of zero in

Anyone with a counting board also has zeros, as empty places with no counters, and ancient people had no problem understanding and using the concept of zero in calculations (though most probably would not have considered zero a “number” per se). They just didn’t write explicit zeros in their permanent serialization format. But there are certainly plenty of mathematical ideas and tools ancient people didn’t know about: they didn’t have a convenient method of manipulating algebraic expressions and equations; they had only the most rudimentary version of differential/integral calculus; they didn’t have group theory, linear algebra, complex analysis, etc.