Answer:

historian

Answer	Crossword Clue
HISTORIAN	Arnold Toynbee, for instance.
HISTORIAN	Commager is one.
HISTORIAN	D. S. Freeman, for instance.

HISTORIAN	Calling of Arthur Schlesinger Jr.
HISTORIAN	Gibbon, for one.
HISTORIAN	Commager or Beard
HISTORIAN	Paleologist
HISTORIAN	Expert on eras
HISTORIAN	Good person to ask "What happened?"