The Holy Roman Empire
Overview, including rulers, structure, and maps

The Holy Roman Empire
Survey from Wikipedia

Otto the Great
The first Holy Roman Emperor

The Investiture Controversy
Epic struggle between Henry IV and Pope Gregory VII

The Concordat of Worms
Another in a long line of attempts to solve the problems between the Empire and the papacy

Frederick Barbarossa
Perhaps the most famous leader of the Empire

The Golden Bull of 1356
Famous proclamation by Charles IV that changed the empire into an election-based entity

The End of the Middle Ages in Europe: The Holy Roman Empire
Focuses on the 14th through 16th Centuries

Reichstag
Gathering of government leaders

The Peace of Augsburg
Religious settlement precipitated by the rise of Lutheranism

The Thirty Years War
Devastating series of battles that consumed Europe from 1618 to 1648

The Treaty of Westphalia
Background and context of the famous treaty that ended the dynamic 17th Century European wars

The Confederation of the Rhine
Napoleon's reorganization of the Empire

Imperial Free Cities
It wasn't an oxymoron.