Silt

I'm a castle under waves.
You wash away the surface
'Til not a granule remains.
The waves crash in the moonlight,
And over grainy land,
Eroding and erasing,
The delicate palace of sand.
The sun will rise in morning,
On the shore I will not be.
The tide took every particle,
And dispersed me in the sea.
When the water pulls away,
And the murky waves will cease,
I will layer my foundation,
Piece by tiny piece.
For I am like a castle,
Diminished to salt and silt,
I am easily dismantled,
Yet, easily rebuilt.