expression, noun-modifying (irregular)
extending over many years; spanning several years
Rare, formal expression used as a prenominal modifier to describe something that lasts or continues for a long period of years. Often found in written or literary contexts.
幾年にもわたる研究の末、ついに新薬が完成した。
After many years of research, the new drug was finally completed.
これは幾年にもわたる努力の結晶だ。
This is the fruit of many years of effort.
More common and neutral expression for 'over many years'; 幾年にもわたる is rarer and more literary.
Phrase composed of 幾年 (many years) + に (particle) + も (emphasis) + わたる (to extend over). The exact origin is transparent from its components.