Specifically, he implemented the seminar teaching method in his classroom, and focused on archival research and analysis of historical documents. Beginning with his first book in 1824, the "History of the Latin and Teutonic Peoples from 1494 to 1514", Ranke used an unusually wide variety of sources for a historian of the age, including "memoirs, diaries, personal and formal missives, government documents, diplomatic dispatches and first-hand accounts of eye-witnesses". Over a career that spanned much of the century, Ranke set the standards for much of later historical writing, introducing such ideas as reliance on primary sources, an emphasis on narrative history and especially international politics (). Sources had to be solid, not speculations and rationalizations. His credo was to write history the way it was. He insisted on primary sources with proven authenticity.