It is shown in Marno's flashbacks that the Brierclock was built more than 1,000 years ago, before the War of the Gods. It was a tall tower with a clock in the top located in Cujam, the hometown of Wiseman. People in Cujam used to jump from the top of the Brierclock without using thier Wings of the Heart as a test of courage. After the War of the Gods, when the Earth becomes polluted and the continents rise to the sky, Cujam becomes Sheratan in Hassaleh, and the Brierclock stays in its place, slowly getting covered by thorny plants.
Later in the game, Sagi uses the Brierclock as a trigger for releasing Marno's memories, and thus, travelling between his age and the Age of the Gods at will.