Why do verbs ser and ir have identical conjugations in the preterite?

Verbs ser and ir are, as we know, different verbs in Spanish. Here are both verbs conjugated in all six persons, in the present tense:

Ser, presente

Soy

Eres

Es

Somos

(Sois)

Son

Ir, presente

Voy

Vas

Va

Vamos

(Vais)

Van

Many students find it shocking to learn that, in the past tense, both verbs are identical:

Ser, pretérito perfecto

Fui

Fuiste

Fue

Fuimos

(Fuisteis)

Fueron

Ir, pretérito perfecto

Fui

Fuiste

Fue

Fuimos

(Fuisteis)

Fueron

And they ask: “How can this be?” Well, there is an explanation: Spanish developed from Vulgar Latin, which was brought to the Iberian Peninsula by the Roman soldiers during the Second Punic War (3rd Century BC). In Classical Latin, the equivalent verbs for ser and ir (esse and ire, respectively) did have different past tenses, but Spanish, as it developed from a not-so-well-spoken version of the ancient language, took the Latin past tense for esse (ser) and applied it to both verbs ser and ir, ignoring the original Latin past tense for ire.

Isn’t that interesting?