The Elder Scrolls Online: Tamriel Unlimited will be free to play from April 11 to April 18. This free play event will allow unrestricted access to the base game and will offer 500 Crowns (in-game currency) to spend.
During the free week, both The Elder Scrolls Online: Tamriel Unlimited and The Elder Scrolls Online: Gold Edition will be on sale. Normally they're priced at $30 and $60 respectively.
And if you buy the game during or after the week, you'll get to retain all the progress from the free week.
For more info visit the official site.