Why the second “は“ in this sentence?


Why is there a “は” after 以前 in the following sentence? I would have guessed it
would read 以前 by itself or 以前に。

人々は人間しか言語を使えないと以前は考えていた。 People used to think that only humans could use
language.

Found this sentence from the Examples in the dictionary app Midori.

Many thanks in advance! Paul

