An overview of the various eras:

1. The Dawn Era - The birth of time itself. Different from the Merethic Era.
2. Mythic Era or Merethic Era - Includes creation of Time and Nirn, the Aedra, Daedra and the races of Tamriel.
3. The First Era - Includes both the First and Second Empires. (The First Empire, either the Ysgramor Dynasty of Skyrim or the Alessian Empire, the Second, the Reman Dynasty)
4. The Second Era - Also known as the "Common Era", includes the rule of the Akaviri Potentates, as well as the 400 year time period known as theInterregnum. The Elder Scrolls Online and Redguard take place in this era.
5. The Third Era is the Empire of Tamriel, ruled by the Septim Dynasty, and lasts 433 years. Arena, Daggerfall, Morrowind, and Oblivion all take place during this era.
6. The Fourth Era is the era that occurs after the end of the Septim Dynasty, and includes the events in Skyrim.