What does particle を mid sentence without a verb mean?


I'm reading a magazine article and I've come across a sentence that I'm not
too sure about.

> そんな濃密な5年間を、記事担当のコラムを交えつつ振り返る。

I think the sentence means something like "These rich 5 years will be covered
in the article" (very rough inaccurate translation). But I don't really
understand this question grammatically. Why does the first clause not end with
a verb but just particle を?

I'm also not too sure about the second part, "the column in charge will look
back on [these rich 5 years]" is probably my best guess. But I'm really
confused about the 交えつつ振り返る, "with mixing looking back"




The grammar here is a bit more complex, and it looks like that's confused you.
Let's take a closer look at this structure.

> そんな濃密【のうみつ】な5年間【ごねんかん】を、記事担当【きじたんとう】のコラムを交【まじ】えつつ[振り返る]【ふりかえる】。

There are a few things going on here. If we diagram it a bit differently, it
might become more clear what's going on.

> ５年間を 振り返る。  
>  そんな濃密な  
>  コラムを交えつつ  
>  記事担当の

  * The simplest core of the main statement is that top line: ５年間【ごねんかん】を[振り返る]【ふりかえる】 ("to look back on [those] five years"). That's where that を fits in -- it marks the object of the verb [振り返る]【ふりかえる】.
  * The second line is a modifying phrase, used to tell us more about what kind of ５年間【ごねんかん】 we're talking about: そんな濃密【のうみつ】な ("those rich and full / jam-packed ...").
  * The third line is the simplest core of the embedded sentence: コラムを交【まじ】えつつ ("while mixing in [newspaper?] column [content / articles / pieces]"). This has the ～つつ ending, telling us that this action is happening alongside, or in a subordinate way to, the action of the main statement.
  * The fourth line is another modifying phrase, telling us more about what kind of コラム we're talking about: 記事担当【きじたんとう】の ("belonging to the person in charge of articles" → "the editor's").

Putting it all back together, we might translate this as something like the
following. This assumes that the context is a newspaper, magazine, or similar
medium, that would have a regular feature section, in which this text appears.

> We look back on those jam-packed five years, with a mix of columns from our
> feature editor.

