When Elizabeth succeeded to the throne in 1558, Dee became her astrological and scientific advisor, even choosing her coronation date. From the 1550s to the 1570s, he served as an advisor to England's voyages of discovery, providing technical aid in navigation and political support to create a "British Empire", a term he was the first to use. Dee wrote in October 1574 to William Cecil, 1st Baron Burghley seeking patronage. He claimed to have occult knowledge of treasure in the Welsh Marches and of valuable manuscripts kept at Wigmore Castle, knowing that the Lord Treasurer's ancestors came from the area.