Rewrite this in correct form: Based on several

Hmmm... Kpadam! Interesting!
Lets hear what's your rationale.

Kpadma, "basing the belief... historians believe..." is redundant. Furthermore, "basing the belief" is not proper english.
You can "infer something based on the belief that" but you cannot "basing the belief on X... and infer something else"

basing belief does sound unidiomic. How about..."Using manuscript"

but paul, I am asking you all to explain what is wrong with the original sentence

This sentence seems fine to me and I don't think there is much correction to be brought to it. The modifier "Based on several manuscripts that date back to middle ages" properly modifies "historians" because it is "historians who, based on several manuscripts ..., believe that...".
I think the potential error lies in the last half of the sentence "Charlemagne first rose to power as a mere teenager." I think it should be re-written as "Charlemagne first rose to power when he was a mere teenager". When is a better descriptor as a referal to a specific point in time when Charlemagne rose to power than as would be IMO. Correct me someone if I'm wrong

Official answer per my source is:
Using several manuscripts that date back to middle ages, historians believe that Charlemagne first rose to power as a mere teenager.

I still did'nt quite understand why the original sentence is wrong. Can anyone explain...or give it a shot?

Mirhaque, you really wanted to mislead us all here without posting the choices didn't you? Reading the official answer, It is now much clearer that the original sentence is wrong because it is as if "historians" that were "based on several manuscripts...."
The correction should be "historians", themselves completing the act of "using several manuscripts..."

Based on <Something_1>, historians believe that <something_2>
Historians are based on <sometime_2> << Inocorrect.

Basing <something> on <something2>, historians ...
Historians based <something> on <something1> << correct.

I would rewrite as follows:

1) Historian believe, based on several manuscripts that date back to middle ages, that Charlemagne ....

or

2) Using several manauscripts that date back to middle ages as their basis, historians believe.....

Great points by AkamaiBrah.

My quibble is that one doesn't "believe using manuscripts."

One digs using a shovel, sure, but the manuscripts aren't a tool for believing.

Scientists have conjectured using manuscripts.
They may have even hypothesized or assumed, but they don't use manuscripts for believing.

Yes, but I said:

"Using manuscripts as their basis"

There is quite a bit of difference between saying:

Using the works of Haydn, Mozart composed his greatest sonatas.
Using the works of Haydn as his inspiration, Mozart composed his greatest sonatas.

Just as one can use something as the inspiration for a composition, one ought to be able to use something as the basis for a belief.

In addition, I don't see your distinction of why manuscripts cannot be used as a tool for believing, yet can be used for conjecturing, hypothesizing, and assuming. Also, if one assumes something, i would conjecture that he or she also believes it.

Doesn't it seem conceivable that someone might use a few manuscripts as a basis to form a conjecture, a few more to formulate a hypothesis, a few more to create a belief, and finally a few more to create a belief so strong that it is universally assumed.