who were the equestrians?

[Emerodius]

So i want to know where exactly do they fall in the Patrician/Plebeian Spectrum? I know that originally they were pople who posessed a horse and served in the cavalry but what about towards the late republic/early empire era? I always thought that Equestrians were (at that point) were mostly people who were of plebeian ancestry but had managed to make money and thus were enrolled in the equestrian order. is this rifght or wrong? Were they allowed in the senate? were they considered a subset of plebs and thus were their interests represented by the Plebiean tribune?

[Epictetus]

I don’t think there is a complete consensus and historians are still arguing. We can figure out some things, though. For one, the knights were generally considered in the aristocratic order along with the patricians. T.J. Cornell points out that horses and aristocrats go together simply because of the money and time necessary for horsemanship. More explicitly, see Cicero in his discussion of the Roman constitution:

There is much advantage in the harmonious succession of ranks and orders and classes, in which the suffrages of the knights and the senators have their due weight.

Cicero, The Republic, IV.2.

Moreover, as far as I can determine there were no knights whatsoever involved in the plebeian successions. They were firmly entrenched with the ruling class and they did serve in the senate.

But yes, some knights were originally plebeians:

…having created a great number of knights from the common mass of the people…

Cicero, The Republic, II, 22.

During the so-called “Closing of the Patriciate” this could be a method of upward class mobility, I presume.

This is confusing, but we have to be careful about thinking of a rigid, unchangeable class structure. Cornell goes on to say:

The important point is that in most cases these distinctions do not coincide, but represent contrasts between different kinds of groups. We are dealing with a pattern of overlapping and intersecting status categories, characteristic of a society that was sufficiently complex for the same person to belong to several different groups at the same time, and in which there was a very large range of possible combinations.

Cornell, Beginnings of Rome

[Nathan Ross]

where exactly do they fall in the Patrician/Plebeian Spectrum? I know that originally they were pople who posessed a horse and served in the cavalry but what about towards the late republic/early empire era?

It's worth mentioning that by the late republic the old patrician/plebian distinction didn't have much political meaning - there were very few patrician families left by then, and aside from their being unable to stand for the office of Tribune of the Plebs, there wasn't much difference between them and the plebian families, aside from residual social snobbery...

I always thought that Equestrians were (at that point) were mostly people who were of plebeian ancestry but had managed to make money and thus were enrolled in the equestrian order. is this rifght or wrong?

That's right, I'd say. By the late republic, the equestrian and senatorial orders collectively formed the aristocracy of Rome - they were the wealth and property elite. Senators were officially forbidden to engage in trade, so their wealth supposedly came from land ownership. The equestrians were free to enter business - often on behalf of their senatorial relatives.

Were they allowed in the senate?

Sons of senators were entered into the equestrian order, until such time as they gained a first magistracy and then entered the senate (which involved surrendering their equestrian status). Similarly, equestrians could, if they had the money and connections, run for election as well. So there was much fluidity between the two 'orders' - later emperors frequently 'adlected' (promoted) deserving equestrians into the senate, as a mark of favour.

Lacus Curtius has a very detailed appraisal of the equestrians here:

Smith's Dictionary - EQUITES

- Nathan