And it shall be for a sign, and for a witness unto the Lord of Hosts in the land of Egypt."[17] Two brothers, archaeologists John and Morton Edgar, as personal associates and supporters of Russell, wrote extensive treatises on the history, nature, and prophetic symbolism of the Great Pyramid in relation to the then known archaeological history, along with their interpretations of prophetic and Biblical chronology. They are best known for their two-volume work Great Pyramid Passages and Chambers, published in 1910 and 1913.[18]