For full context: https://www3.nhk.or.jp/news/web_tokushu/2018_0202.html?utm_int=news_contents_news-closeup_002
The sentence in question: 山田さんによると、八王子は何度か大規模な火災に見舞われ、戦時中は大規模な空襲も受けたことから、古い資料なども多くは残っていないということで、江戸時代の隕石を探すのは容易ではないと話していました。
My attempt at translation: "According to Mr.Yamada, Concerning Hachioji, He said that because it was struck with large scale fires several times and also suffered air raids during war, there not being left many old documents, the search for a meteorite from the edo area won't be simple."
I really have no idea why this は in 多くは (bold) is at this very position. I also have no idea why it has to exist in this phrase at all, and therefore I also don't know what it does and just translated the sentence as if it wasn't there xD