From Susan Cooper's The Dark is Rising Sequence, The Grey King.
On the day of the dead, when the year too dies,
Must the youngest open the oldest hills.
Through the door of the birds where the breeze breaks
There fire shall fly from the raven boy,
And the silver eyes that see the wind,
And the Light shall have the harp of gold.
By the pleasant lake the Sleepers lie,
On Cadfan's Way where kestrels call,
Though grimm from the Grey King shadows fall,
Yet singing the golden harp shall guide
To break their sleep and bid them ride.
When light from the lost land shall return,
Six Sleepers shall ride, six Signs shall burn,
And where the midsummer tree grows tall
By Pendragon's sword the Dark shall fall.
Y maent yr mynyddoedd yn canu,
ac y mae'r arglwyddes yn dod.
Now, supposedly, "Y maent yr mynyddoedd yn canu, ac y mae'r arglwyddes yn dod," means something like "The mountains are singing and the lady comes." But, there's some grammar errors in there that may change the meaning, too.