Helical Annexes

The Helical Annexes are that class of subsidiary structures in The Tower whose floor-plates are wound, rather than stacked, about a central axis. Unlike the main ascent, which proceeds floor by numbered floor, a helical annex returns over itself: to walk its full length is to pass repeatedly above and below the point of entry, each circuit offset by a fractional floor. The class was first given standing in the Annexes of the Third Concordance, which separated the helical from both the Void Annexes and the Organic Annexes and assigned to the former a distinct register of survey and a lighter grade of seal. The western examples are administered from Floor -2,147 at the West Spiral Repository; the eastern examples answer to no single office and are catalogued ad hoc.

Helical annexes are not a design preference but a consequence of their siting. Where a vertical void of more than eleven storeys presented itself, the builders of the Third Concordance period were forbidden to bridge it directly, and so ran their floors around it instead. The resulting structures are classified under the Spiral Decimal System, which measures a void in spiral units — the number of full circuits needed to close a given aperture — and files each annex under a decimal designation of three figures.

Anatomy and nomenclature

A helical annex consists of a gallery, one or more staircases, and a landing apparatus. The gallery is the habitable band; the staircases are the means of ascent; the landing apparatus is the much-amended set of rules governing where one may stop. The finest surviving example is the Seventh Helical Gallery, a longitudinal atrium spanning Floors 22. through 22. of the Western Helical Staircase habitation annex. Its neighbour, the second structure of the same name, is the subject of the long-running Title Dispute, which the Prefect of Juridical Annexes has declined to hear on four occasions.

The East Helical Staircase is the principal eastern example, and its condition illustrates the general hazard of the type. Helical Variance — the progressive warping of spatial perception and memory that afflicts those who ascend helical stairs without an external reference — is endemic there and is the reason for the posting of a counter-rotational observer at every third landing.

"No ascent of a helical annex shall be undertaken on recollection alone. A clerk who believes himself to have climbed four circuits has, in the Registrar's experience, climbed either three or five."

— Annexes of the Third Concordance, Annex 7, clause 2

Administration and the Selvage Question

Because their lengths are not commensurate with their floors, helical annexes generate a surplus: short sections of gallery that close a circuit but belong to no numbered storey. These are the selvages, and their disposal has been contested since the Textile Repository asserted, in a memorandum of 8 Floreal, that selvage management falls naturally to it under the Selvage Decimal System, the repository's own classification of edge-matter. The West Spiral Repository answered that a selvage is an architectural residue and not a textile, and that the Textile Repository's claim rested on a false etymology. The question remains open. In practice the selvages are swept by whoever is nearest and recorded by the Supporting Annexes under a provisional heading that no one has yet had authority to retire.

The Algorithm of Shifting Annexes has been applied to the selvages on three occasions, each time reclassifying them as competent annexes in their own right and each time being reversed on appeal by the Commission on Annexes and Outliers. The reversals were not identical, which has made the precedent difficult to cite.

Construction materials and the Seventh Quarries

Helical galleries require a stone that will tolerate curvature without spalling, and the porous grey limestone of the Seventh Helical Gallery quarries has been the preferred material since the affected section of the Western Helical Staircase was rebuilt in it. The quarries lie within the gallery they supply, which has caused two separate disputes over whether extracted stone counts as an annex of the annex. The survey office maintains that it does not; the quarry ledgers, which have never been reconciled with the survey, suggest otherwise on eleven pages.

Maintenance is by circuit rather than by floor. A crew assigned to a helical annex is assigned to its whole length and must complete the circuit before rest, a provision that has produced at least one recorded instance of a crew continuing to climb for two days after the annex had ended, under the impression that the final landing was a landing of passage. The incident is recorded without comment in the Helical Manifold of Partial Echoes, which is itself thought to be a helical structure of indefinite length.

Disputed classification

Scholars disagree on whether a helical annex may properly be said to possess a floor number at all. The Annexes of the Third Concordance holds that it may, since every part of the Tower has a number and the spiral merely complicates the route. The Fourth Recension of the same document, which survives in three fragments and a summary, holds the contrary: that a helical annex is continuous and therefore unnumbered, and that the numbers commonly assigned to its landings are conveniences of the survey trade and not designations of the Tower. The West Spiral Repository has never ruled on the question, on the grounds that a ruling would require it to decide which recension is authoritative, and that no one has asked it to do so in writing.

Pending a ruling, the annexes are numbered as though the first view were correct and surveyed as though the second were. Every helical annex in the Tower therefore has a number, a spiral designation, and a standing note in the register reading: number provisional.