The preferred building material in Gehennum is timber, which is, after all, plentiful and cheap. The Gehennese use stone for fortifications and (increasingly through the period covered by this description) the more magnificent and grandiose buildings.

In the Archaic Period there are many relatively recent city walls built in 'polygonal' style (like Inca or Mycenaean walls) and quarry-faced stone. New work is, however, mostly being done in ashlar (highly-dressed rectangular blocks). Limestone is the most common building stone, and this in Gehennum tends to be fairly soft and porous. Marble is used for magnificent effect, especially in temples, and some cities make extensive use of basalt. Masonry is mortared with sand-lime cement, and sometimes this is mixed in with the rubble cores of thick (eg. fortification) walls, forming a type of (relatively soft) concrete.

Timber buildings are often very large and heavily carved, and employ many different and sophisticated truss designs to provide covered spaced free of pillars. Stone buildings' roofs are usually supported by timber frames and trusses.

In the Classical Period Gehennese builders gain access to hydraulic cement (which will set under water, and is very durable). This is used to make a more durable mortar, and also in a more extensive use of concrete, for example in building foundations, piers, and sometimes buildings and fortifications.

At about this time Gehennese architects start to use arches, domes, and barrel vaults with some freedom, and build huge, light cantilevered timber roofs, covering vast interiors.

In the Decadent Period groin vaults appear, but the Gehennese are still using only round arches, and therefore can only vault over square areas. Concrete buildings with thin veneers of expensive decorative stone are becoming common, and different sorts of rubble are being used to make concretes with different properties (basalt for strength, tufa and even pumice for lightness). With these materials, architects are building large self-supporting concrete domes.

Civil engineering

To be brief, Gehennese civil engineering in the Archaic Period is as good as that that the Ancient Greeks used, which is very impressive. The Gehennese will tunnel through a mountain to get a water supply where it is needed, if that is what it takes. They can also dredge harbours, force passages through coral reefs, and build extensive irrigation and drainage systems.

In the Classical Period and later, Gehennese civil engineering is simply awesome. Gehennese civil engineers have all the technique of the Romans, are wealthier, and have a readier supply of labour. Harbour works, storage dams, aqueducts, irrigation schemes, bridges, and the terracing of slopes for paddyfields: engineering works transform the landscape.

Naval architecture

The design and building of boats and ships is, perhaps, the only field in which Gehennese technology is not at the forefront of the World of Isles. Then, perhaps, it is just that the Gehennese builds ships that are suitable to their special conditions.

The internal waters of the Gehennum archipelago are sheltered from ocean waves and are usually becalmed. So Gehennese vessels do not need great stability and high gunwales. Rather more often, they need oar-ports and outriggers for their rowlocks. Also, when they do sail, it is usually coasting on the land or sea breeze, with the wind on the beam strong and steady. So the lateen sail (like that of an Arab dhow) is very suitable, even though it is unhandy and won't let one sail close to the wind.

Gehennese civilian vessels, cargo ships, fishing boats, and passenger barges are lateen-rigged on a single mast, low, and equipped with sweeps for rowing. Their hulls are no stronger than is necessary for their comparatively light duties.

Gehennese warships are no more robust, but they are rather more exactingly engineered. They are built for speed under oars: long, light, sleek, and packed with rowers.

In the Archaic Period open galleys with thirty to fifty oars are still common, and outside the Central Isles they often have no rams. The city of Hospis, however, has pioneered the construction of double-galleys with up to 100 rowers in two superimposed banks, and these (invariably equipped with rams) are the main battle ships of advanced parts.

In the Classical Period double galleys are still used as cruisers and consort ships, but the pride of the fleet is in its triple galleys with 170 rowers in three superimposed banks. The rowlocks of the upper two banks are cantilevered well outside the hull on outriggers (not the floating kind), and these also support a fighting-catwalk for the marines. The main weapon of these ships is, however, unquestionably their formidable rams.

It is nothing impressive for a triple galley to reach a speed of 20 kilometres per hour, or to sustain 12 to 13 kilometres per hour for extended stretches.

In the Decadent Period the use of light mechanical artillery (ballistas) and incendiaries at sea is the cutting edge of technology. Huge, full-decked galleys with two men pulling each of the oars in the upper two banks are common, and there is some experimentation with stabilising outriggers and catamarans, that sacrifice speed and manoeuvrability for size and steadiness as a platform for ballistas and even catapults.

Mechanical engineering

Mechanical engineering is what the Gehennese excel at. Even in the Archaic Period they build overshot and turbine-style watermills of high efficiency , which they use for crushing ores, fulling cloth, pressing oilseeds, threshing and polishing rice, working the bellows in foundries and smithies, and countless other purposes. They build catapults and ballistas as well as the Romans, crossbows as good as anything on Earth before the time of Leonardo da Vinci.

In the Classical Period Gehennese mechanics build pendulum clocks, cranes, davits, and windmills. They raise water, and spoil and ore from mines, with endless chains of buckets hoisted by the power of wind and water. Counterweights are widely used in a number of applications, such as for raising drawbridges, portcullises, and gates. Engineers have a quantitative knowledge of the weights and mechanical advantages they must employ.

Some engineers (such as Lykomorphus) apply their expertise to building machines of war, and the greater of these are certainly capable of feats as remarkable as anything done by Archimedes at the defence of Syracuse. For instance, Lykomorphus built an enormous counterweighted trebuchet, capable of throwing missiles over a tonne in weight for distances of four or five stadiums (800-1000 metres) with considerable accuracy, cranes that could pluck a galley out of the water and crush it, and a catapult that threw a line and grapnel to overturn a ship three stadiums (600 metres) out to sea.

Others with a more frivolous turn of mind build marvellous mechanical, hydraulic, and pneumatic devices, that open doors as if by a miracle, dispense measured amounts of holy water when a coin is put in a slot, and the like. For example, pneumatic tubes, operated by bellows, are used to deliver messages, cash, and other small items in some large buildings.

In the Decadent Period mechanics build clocks of fantastic complexity, which play tunes on carillons of bells, and cause mechanical figures to act out brief pantomimes. Eccentric inventors attempt automatic abacuses, submarines, flying machines, and so forth. They also build automatic devices of some complexity, and absolutely fiendish traps.


Like all the peoples of the World of Isles, the Gehennese are short of metals. They use flint, obsidian, and glass for cheap cutting edges, or where mechanical strength is not so important, or where phenomenal sharpness is required.

Weapons edged with stone and glass, sometimes even shell, produce to our minds an impression of primitiveness, but in the case of the tropical peoples of the World of Isle such an impression is by no means accurate. Where the Gehennese do use bronze, iron, and steel they do so with superb craftsmanship.

Bronze, an alloy of copper with expensive tin, is the best metal for casting, and in ancient times was used to make weapons and armour. By the Archaic Period it has been largely replaced by much cheaper wrought iron, which has indeed superior strength and hardness, but has to be worked by laborious smithing and wasteful grinding. In the backward States of eastern and western Gehennum armour and blades are case-hardened and cementated, or sometimes strip-welded, and are up to the standard of Spanish steel of the early Roman empire, or the 'arming swords' of Sweden in the 11th century.

In the more sophisticated Central Isles, iron ore is reduced in a catalan forge, producing a range of compositions from pure iron at the top of the stack to cast iron at the bottom. Steels with different properties are used to make different parts of a blade, and the resulting swords are a match for good mediaeval Japanese specimens.

In the Classical Period composite blades are run-of-the-mill, and the best swordsmiths use a forged ultrahigh carbon steel like bulat or Damascus steel. Good Gehennese steel is strong, tough, and very hard. Swords of merely 'good' quality are a match for anything ever made on Earth. And bulat can also be used to make superb armour without the difficulties of cementating, case-hardening, and quenching large odd-shaped pieces that plagued European plate.

In the Decadent Period all smiths in Gehennum work in bulat, and the best have developed techniques for producing the patterned or watermarked effect of Damascus steel (without compromising the mechanical properties of the steel, either).


Gehennese alchemy is not a mystical and symbolic system like the useless Arabic and European study of the same name. It is practical and empirical, and not burdened with bizarre metaphysical doctrines. On the other hand it does not (during the time detailed in this description of Gehennum) achieve the systematic and quantitative knowledge that would fit it for the name 'chemistry' and listing among the sciences.

Gehennese alchemy is cottage-scale industrial chemistry. It emerges in the Archaic Period from the art of making and mixing dyes and mordants, and develops a number of generally useful techniques for extraction, purification, and separation of chemical substances.

The Archaic Period

The alchemical products of the Archaic Period include dyes, mordants, bleaches, quicklime, slaked lime, soap, perfumes, cosmetics, medicines, poisons, and some specific antidotes. Many of the dyes, medicines, poisons, and antidotes are extracts from Gehennum's diverse rainforest flora, and others from fish and land animals, especially insects and frogs.

Alchemical processes are sometimes carried out on a large scale, such as the burning of coral and limestone in kilns to make lime for mortar, and the lixivation of wood ash to make lye (a mordant and ingredient of soap production).

The Classical Period

By the Classical Period several new processes have been invented, including evaporation, reduction with a forced draught or charcoal, and distillation. New products include hydraulic cement as good as the Romans', oil of vitriol (sulphuric acid), spirits of nitre (nitric acid), spirits of salt (hydrochloric acid), alcohol, laudanum (a tincture of opium), gunpowder, and naphtha (a mixture of combustible oil, accelerants, and phosphorus that catches fire on contact with air and continues to burn in the presence of water. There are also many new dyes, pigments (for paint, glass, and ceramic glazes), medicines, poisons, and antidotes, and perfumes are made using steam distillation.

Several significant alchemical discoveries were made by one man, Lykomorphus (an artist and engineer). Among them were hydraulic cement and naphtha, used in different aspects of his career as an engineer.

For several reasons, the Gehennese do not use gunpowder in firearms. First, they cannot make it in quantity: there are no mineral deposits of saltpeter, and, as animals are not stabled, no dung-heaps. Second, in the humid climate it quickly absorbs moisture from the air, and becomes an inefficient or even ineffective propellant. Third, metal to make adequate cannon would be very expensive compared with even very large mechanical artillery. There have been experiments, usually with wooden-barrelled guns, but they have not been a success. Gunpowder is used in fireworks.

The Decadent Period

The actual art of alchemy in the Decadent Period has advanced by the invention of the mercury process for extracting gold and a few curiousities like the thermometer. The real achievement, though, is the increase of scale. Soap is made, and potable spirits distilled, on a scale that approaches the industrial (though of course using batch processes).


The magnifying effect of lenses of clear glass is known in the Archaic Period, as is their ability to produce high temperatures and ignition by focussing sunlight. Their ability to restore close vision to the aged is known: hand-held magnifying glasses are used to assist reading.

The Classical Period sees the advent of eyeglasses and the compound telescope. Concave lenses are used in telescopes and to correct short-sightedness.

The collapsible, 'telescoping' type of telescope was invented by Lykomorphus.

In the Decadent Period the Gehennese have invented bifocal glasses and a crude microscope, but have not yet produced a transmission microscope.

Copyright © 1988-2004 Brett Evill. All rights reserved.

Copyright © 1991 by Brett Evill. All rights reserved.