Here are two clauses:

a. The main clause, The Romans killed the men

b. The subordinate clause, who were taken

The word who is a pronoun, for it takes the place of the noun men. It also connects the subordinate clause who were taken with the noun men. Hence the clause is an adjective clause. A pronoun that connects an adjective clause with a substantive is called a relative pronoun, and the substantive for which the relative pronoun stands is called its antecedent. The relative pronouns in English are who, whose, whom, which, what, that.

[221.] The relative pronoun in Latin is quī, quae, quod, and it is declined as follows:

SingularPlural
MASC.FEM.NEUT.MASC.FEM.NEUT.
Nom.quīquaequodquīquaequae
Gen.cuiuscuiuscuiusquōrumquārumquōrum
Dat.cuicuicuiquibusquibusquibus
Acc.quemquamquodquōsquāsquae
Abl.quōquāquōquibusquibusquibus

1. Review the declension of is, [§ 114], and note the similarity in the endings. The forms quī, quae, and quibus are the only forms showing new endings.

Note. The genitive cuius and the dative cui are pronounced co͝oi´yo͝os (two syllables) and co͝oi (one syllable).

[222.] The Relative Pronoun is translated as follows:1

Masc. and Fem.Neut.
Nom.who, thatwhich, what, that
Gen.of whom, whoseof which, of what, whose
Dat.to or for whomto or for which, to or for what
Acc.whom, thatwhich, what, that
Abl.from, etc., whomfrom, etc., which or what