the maximum level (of sth. ): the utmost limit (of sth. )
the farthest (upper) limits (of sth. )
the ultimate (in sth. ).
"...Дело Главлита охранять военную и государственную тайну, а не... вмешиваться в литературную ткань произведения... (Аплодисменты. Возгласы с мест: „Верно... Правильно...".) Это вмешательство достигло ныне геркулесовых столпов глупости» (Свирский 1). "...The job of Glav lit is to preserve state and military secrets, not.. to interfere in the creative process." (Applause Shouts from the hall: "That's true, that's right!") "This interference has now reached the farthest limits of stupidity" (1a).
Originally, the name of the two high points of land (the Pillars of Hercules) on either side of the Strait of Gibraltar believed to be "the limits of the earth." According to Greek legend the Pillars were raised by Hercules.
Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. С.И. Лубенская. 2004.