This is the 3809th most frequent Japanese word.
またがる
"またがる" means "to straddle" or "to span."
In this context, 'またがる' conveys the meaning of extending over a period, referring to time or duration.
彼の計画は三ヶ月にまたがる。
His plan spans three months.
In this sentence, 'またがる' functions to describe the act of sitting astride or mounting, particularly onto a horse.
馬にまたがるのが難しいです。
It's difficult to mount a horse.
Here, 'またがる' is used to indicate the idea of spanning or stretching over something, in this case, a bridge over a river.