expression
throughout; over a period of; spanning
Used after a noun indicating a time period, range, or area to express that something continues or extends across that entire span. Often follows words like 長期間, 数年に, 全般に, etc.
See also: 渡る
この研究は10年に渡って行われた。
This research was conducted over a period of ten years.
会議は3時間に渡って続いた。
The meeting continued for three hours.
The verb 渡る means 'to cross' or 'to extend over'; に渡って is the te-form used as a compound particle-like expression meaning 'throughout' or 'spanning'.
The dictionary form にわたる is used attributively before nouns (e.g., 長年にわたる努力 'efforts spanning many years'), while に渡って is the continuative form used adverbially.
Derived from the te-form of the verb 渡る (わたる, 'to extend over, to span'), combined with the particle に. The expression grammaticalized into a compound particle meaning 'throughout' or 'over a period of'.