A historian of ideas must go where his nose leads him, and it often leads him into chilly but not inhospitable regions whose borders are patrolled by men who know every square foot of it. Although I can lay no claim to being a specialist in a particular century or in the classical or medieval periods, my own specialization in the history of geographic thought has forced me to study many periods because their contributions are so great they cannot be ignored. Problems like this must be faced by anyone who wishes to go beyond the narrowest limits. A historian of geographic ideas (especially in the earlier periods) who stays within the limits of his discipline sips a thin gruel because these ideas almost invariably are derived from broader inquiries like the origin and nature of life, the nature of man, the physical and biological characteristics of the earth. Of necessity they are spread widely over many areas of thought.
Clarence J. Glacken, Traces on the Rhodian Shore: Nature and Culture from Ancient Times to the End of the Eighteenth Century, Berkeley: University of California Press, 1967, p. xiii.