There are 3 books in the Tir Alainn Trilogy series. The newest book is The House of Gaian which came out in 2003.

1
The Pillars of the World

Book cover of The Pillars of the World
The first novel in New York Times bestselling author Anne Bishop's Tir Alainn Trilogy.

The youngest in a long line of witches, Ari senses that things are changing—changing for the worse. For generations, her kin have tended the Old Places, keeping the land safe and fertile. But with the Summer…
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2
Shadows and Light

Book cover of Shadows and Light
New York Times bestselling author Anne Bishop weaves a dazzling tale of romance, high adventure, and thrilling fantasy in the second novel in the Tir Alainn Trilogy...
 
Ever since the slaughter of the witches, the Fae—who should be shielding their long-lost cousins from danger—have ignored the needs of the rest…

3
The House of Gaian

Book cover of The House of Gaian
New York Times bestselling author Anne Bishop presents the stunning conclusion to the Tir Alainn trilogy, where the world will be tested in an epic war...

It began as a witch hunt. But the Master Inquisitor’s plans to eliminate all traces of female power in the world have expanded to…