A prothalamion is a celebratory poem written for, or about, an upcoming marriage. Unlike an epithalamion, which honors a wedding on the wedding day or afterward, a prothalamion looks ahead to the event and marks the joy of the approaching union. The form is most closely associated with Edmund Spenser's Prothalamion.
Example
Along the river, music stirs the air;
Two veils of dusk are waiting to be dawn.
We sing before the vows are spoken there,
And bless the footsteps of the bride to come.