Most of the Roman low and medium skill artisans were slaves, actually.

But capitalism is best recognized by the proliferation of commodities, as it is made up of various wage labor capitalist enterprises producing large quantities of fungible goods for market. A chair is a chair is a chair and you can buy 50 varieties of basically the same thing at the furniture store. Under capitalism, all economic life is governed by this: you work a wage labor job and you buy everything else (commodities made by other wage laborers).

Rome did not have such a system. A vastly larger proportion of goods were made at home by oneself or by servants or by slaves. When goods were purchased they would have mostly been produced by slaves or petty bourgeois artisans or apprentices. Wage laborers still existed, but they were not typical.

An important part of Marxist analysis is to focus on the shift from quantitative to qualitative in social development. The high proportion of wage laborers is something that typefies capitalism, but wage laborers have existed for a long time. At some point there was a watershed moment - or watershed many decades - where the material forces that increased this proportion crossed various thresholds to create a new ruling class that became dominant and started throwing their weight around (capitalists). The capitalist class was in no way dominant in Rome.