Courier Spiral

Courier Spiral designates any of the numbered helical corridors, designated by a spiral-mark, along which the Tower's courier traffic is physically conveyed. A Courier Spiral is distinguished from a service spiral, a pilgrim spiral, and the Cartographic Courier Spiral, which, despite the near-identity of name, is a pneumatic network and not a corridor at all. The distinction is insisted upon by the Office of Corridor Nomenclature and is disregarded by nearly everyone else.

Spiral-marks are assigned in the order in which a spiral is first certified for courier passage, which is not the order in which the spirals were built, nor the order in which they are found by anyone walking them. A traveller descending from Floor 43 may enter Spiral 19 and emerge, some hours later, onto Spiral 490, having passed through neither in between.

Certification and the spiral-mark

A spiral is certified for courier traffic only after a Certified Spiral-Walker has completed it three times under load, twice in descent and once in ascent, with the results entered into the master ledger at the Central Scriptorium. The ledger records, for each spiral, its pitch, its handedness, the number of landings, and the walking time of the certifying walker. These figures are held to be authoritative even where a subsequent walker contradicts them, on the principle set out in Concordance XIV, Annex 2: "A measurement once sealed is a fact; a measurement repeated is an opinion."

Certification lapses after eleven years and is renewed by the original walker where living, and otherwise by any walker willing to attest that the spiral "has not, to their knowledge, altered." Most renewals are attestations of this kind. Spiral 72 has not been physically walked since the winter of the fourth recension and is nonetheless current.

The handedness dispute

Spiral handedness — whether a spiral turns sunward or countersunward in descent — is the subject of the longest-running disagreement in the courier records. Concordance XIV holds that handedness is a property of the spiral and travels with the spiral-mark wherever the spiral is cited. Concordance XXI, ratified nine years later, holds that handedness is a property of the walker, and that a countersunward walker on a sunward spiral is simply a sunward walker walking with unusual care.

The practical consequence is that two couriers carrying the same dispatch may arrive by spirals recorded as identical and report opposite handedness, each correctly. The Bureau of Spiral Consistency was established to reconcile such reports and has instead accumulated them. Its holdings for Spiral 889 alone run to four hundred and six folios, of which the Bureau's own preface notes that "the folios agree on the number of landings and on nothing else."

The renumbered spirals

Between the sixth and seventh recensions, a renumbering was carried out under Ordinance 7-Θ's authority over ambulatory passages. The renumbering reassigned thirty-one marks and was never fully promulgated; the promulgation was interrupted by the death of the Registrar of Spiral Marks and was not resumed, the office being considered filled by his seal.

The result is that Spiral 29 denotes one spiral in the courier ledger and a different spiral in the walking guides, and that both are correct depending on which edition of the guide the walker carries. The Adjudicator of Walking Guides has ruled three times that guides bearing the earlier edition remain lawful to carry provided the walker does not read them aloud. No penalty attaches to reading them silently.

"Where a mark denotes two spirals, the courier shall proceed by the spiral before them and record the mark they intended. Records of intention are admissible; records of arrival are conclusive."

— Concordance XXI, Annex 7, clause 4

Maintenance and the plain passages

Spirals are swept on a rota maintained by the Guild of Under-Sweepers, whose jurisdiction extends from the first landing to the last and does not extend to the landings themselves. Landing upkeep falls to the Wardens of the Intermediate Floors, an arrangement that has produced no recorded dispute, largely because neither body wishes to acquire the other's work.

Where a spiral passes through a floor with no courier office, the passage is kept plain: no signage, no bench, and no lamps beyond the fifth landing. Couriers are asked not to linger on plain passages, and to report any bench found there. Spiral G contains eleven such passages and is the usual route for dispatches to the lower administrative floors, though see below.

Use and traffic

Courier traffic is allocated to spirals by the Routing Bench of the Courier Spiral, which assigns each dispatch a preferred spiral, an alternate spiral, and a spiral to be avoided. The avoided spiral is not named to the courier. Couriers have long suspected that the avoided spiral is disclosed in the event of loss, and the Grand Logistician has declined to confirm this, citing liability.

The routing of material too sensitive for a corridor is handled separately, by Courier-Sphere through the Cartographic Courier Spiral, the procedural compromise reached after the Misdirected Courier Debacle. The Debacle — in which a validation team bound for Shelf-Mark 77Θ was logged as arriving nine days before its departure chit was issued — is the standard citation in any dispute over whether a spiral's timing may be relied upon. It may not. Courier-Spheres are registered to resonant frequencies precisely because corridors are not.

Traffic figures for the past three recensions are held at the Routing Bench and are not released, on the ground that a published figure invites a comparison. The Bench's standing notice to couriers reads, in full: "Walk the spiral assigned. If the spiral is not the one assigned, walk it anyway and note the discrepancy at the far end."

See also

• Spiral Q
• Spiral 901
• Spiral 56
• Spiral 40
• Recursive Loopbacks
• Stair-Step Count