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beginning (of a century, etc.)
この城は13世紀初頭に築かれた。
This castle was built at the beginning of the 13th century.
明治初頭、日本は大きな変革を遂げた。
Japan underwent major reforms in the early Meiji era.
その小説は20世紀初頭の日常を描いている。
That novel depicts daily life at the beginning of the 20th century.