素晴らしいcalligraphyを素晴らしいものたらしめているのは何かについて学んだ。
I studied what makes great calligraphy to be great.
With regard to たらしめる I don't understand that sentence structure. The presence of を means there must be a transitive verb in play (たらしめる?). But, what is もの doing there?
Basically, with regard to sentence structure, what part of speech is "もの"? What does it modify or what is it modified by?