The Fallen Nephillim: Bones of the Earth

From the introduction:

Long ago, servants of the gods took mates from the mortal races of the land. Some of the children of these unions became the Nephillim, great giants of immense power. As some of these Nephillim rebelled, lost great duels, or failed in some divine quest, they fell from the sky, crashing into the earth and leaving their great skeletons in buried monument. Even so, their might was such that a glimmer of their being lived on, even in this reduced and imprisoned state.