An Arbiter is tall, a head and more above a tall Human, in long, heavy robes of ink-black and parchment-white, edged with gold and the crimson of an oath’s blood. Its face is hidden, or hard to see, in the shadow of a deep hood, and only a pale line of chin and mouth shows. It carries a pair of scales made of clear crystal, which hang level in its hand, and a crystal gavel. When it walks its steps sound like a slow, regular drum, and when it speaks a sentence writes itself in glowing script on the air beside it. The gavel’s fall rings like a bell, and the ring goes on a long time. Near an Arbiter the air smells of wax and cold stone.

They sit in the courts of the Binding Song, halls of glowing script and walls of laws, and go wherever a dispute over an oath is brought to them.

An Arbiter judges. It hears both sides, weighs the words actually spoken, not what was meant, on its crystal scales, and gives its judgement in a single sentence, which then binds. It is neither kind nor cruel, and it cannot be argued with once the gavel has fallen.

Its scales weigh words: a true account sits level, a false one tips them. Its judgement, once given, binds the parties across all planes, as every promise made in the Song does.

Visitors come to the Song to resolve disputes, and the Arbiters are why. Their danger is that a judgement against a visitor is as binding as one in their favour, and the visitor cannot leave the plane until it is kept.

Some lords and temples on Caeldon make oath-takers swear on scales, and travellers' tales of the Arbiters are sometimes given as the reason. The judges of the Song are said by some to be the Song’s own gods of oath; they are beings of the plane, and judge for no god.

A warning-tale tells of an oath-breaker who fled the Song’s judgement back through a judgement hall’s gate, and of the Oath-Breakers that came through after him and hunted him across three lordships until the debt was paid.