Sentence Correction

Before Budapest was Budapest, it was Aquincum, a Celtic settlement that would go on to become the Roman capital of Lower Pannonia.

A) Before Budapest was Budapest, it was Aquincum
B) Before there was Budapest, it was Aquincum
C) Before it was Budapest, it was Aquincum
D) Budapest was once what was called Aquincum
E) Budapest had been known as Aquincum

OA = A

"Before Budapest was Budapest" seems redundant, but it's actually OK if we're playing on two senses of the word Budapest, as we are here. What the sentence is really saying is something like

"Before Budapest the region was Budapest the modern city, it (Budapest the region) was Aquincum."

This is perfectly fine - short, clear, and grammatical - so A is our answer!

Looking at our other options

B: "Before there was Budapest" ... before where was Budapest? Not clear
C: What's "it"?
D: No need for a double 'was'; we'd just say "Budapest was once called Aquincum"
E: Inappropriate past perfect, we'd just say "Budapest was known as Aquincum"