The bridge and causeway are vitally important to us all. It is the only safe way to travel between the worlds. The straights are notoriously untrustworthy and dangerous, often fatally so. In the sea between the worlds, nothing can be relied upon. Sailing boats are suddenly becalmed or blown uncontrollably off-course. Engines or thaumatological forces will fail without warning during any attempted crossing. Mysterious storms, dead spots, a whole clutch of vicious sea serpents and kraken - these days, few would willingly chance the crossing by sea.
Flying is fraught with its own dangers, and with even more chance of a fatal result. Both aircraft engines and levitation spells will disintegrate catastrophically whilst attempting a crossing, while kites and gliders are at the mercy of any of several large species of dragon. Take my advice: don't ever attempt a passage this way.
With all these fearsome obstacles, some might question the need for the Guardians at all. The answer is plain enough. Since the bridge is the only route between the Two Worlds, our task is to prevent the import and export of Proscribed Goods and Beasts, in accordance with the ancient edicts handed down by the Mages' Convention.
Now, it is not our business to prevent Travellers from crossing between the worlds, in either direction. Whatever your mission, your purpose, we will not impede your progress, except in those very few case where the Master Mages of the Board of Control have banned an individual from passing between the worlds. We police only the crossing itself, not what you get up to on the other side.
A Guardian acting as a soldier is almost unheard of these days, I'm pleased to say. The Old Bridge has witnessed invasion forces, twice from Mundane to Magic and once from Magic to Mundane, as ill-advised or perhaps merely deranged leaders sought to impose their will on the other world. All these attempts ground to a halt after only a few hours, as either the invaders from Magic found they had no defences against cannon and machine guns, or the invaders from Mundane were beset by fireballs and other directed magical energies that can be manifested by even the most junior Guardian thaumaturge.
Ever learning from their experience, the authorities in both worlds have installed traps - gaps in the fabric of the bridge where the roadway could be rapidly removed, cutting off the only route. On the Mundane side, the trap is covered with stout planks of wood, now so worn and scuffed as to be indistinguishable from the surrounding stonework, with strategically-placed explosive charges which would drop any invader into the sea at the touch of a lever.
On the Magical side, the trap is floored with pure magic - translucent orange which flows and scintillates incessantly, and through which the waves are clearly visible far below. Walking over the magic floor is considered a test of will for Mundane Visitors - a few cannot bring themselves to step onto the gap, and are therefore forever unable to enter the world of Magic.
Our day-to-day work is to watch, to inspect travellers and their transport to detect and confiscate contraband. Of course we employ a whole gamut of magical means of detection, but so often we rely on our intuition - the Guardian's 'nose' for Travellers with something to hide. I understand the Guardians on the other side have different, technological means of detection, although frankly I have no idea how these so-called 'metal detectors' work.
There is a certain amount of trade that makes its way across the Old Bridge, since a few things manufactured in the Mundane world are useful in the world of Magic, and vice versa.
As you already know, in this world, few machines work reliably - or at all. Simple machines like wheels work perfectly, but smaller ones, like wristwatches, will just stop. And your wondrous electronic machines fail immediately - your mobile phones and computers become dead and inert lumps within seconds of crossing the bridge. I hope you have all left such devices at home!
Even so, some machine-made products - like paper and spectacles - are widely used in the world of Magic. And certain items of food and drink are hugely popular - I myself am definitely partial to the occasional glass of your Champagne!
Certain magical items, too, seemed to have some efficacy in your world, particularly where the effect is, shall we say, diffuse and psychological. Stimulants, love potions, good luck charms - all of these have willing takers in the Mundane world - and whether these effects are real or merely in the heads of the customers: well who am I to say?
Tourism is a major reason for Travelling, and more of your people than ever are braving the crossing. I dare say most of you are here today as Visitors to sample the diversions of the world of Magic. If this is your first time, well, an especial welcome to you. You may think at first that you have come to a world where, to your Mundane eyes, society appears to be stuck in a version of the late Middle Ages. But look closer, and those hidden sophistications enabled by Magic will, I feel sure, both charm and delight you.
Of course, tourists Travellers visit your world as well. People from the world of Magic are amazed and astounded by your devices, your technology: instant communications, mobile phones, your skyscrapers and your high-speed transport by road, rail, and air.
There's also a certain amount of more human-focussed trade from Magic to Mundane. Maids, labourers, gardeners, even prostitutes - many poor people travel to work in Mundane. Even so, few stay for long, despite the considerable wealth that can be earned over there.
These migrant workers often feel that they are living their lives under a severe handicap. At home, they have become so used to performing actions with thaumaturgics - magic just a word or gesture away - they feel an extreme sense of loss at the core of their very being. And think of those poor souls banished from the world of Magic and forever unable to perform their art.
The combination of trade and tourism means that crossing the bridge is often subject to queues and delays. Part of our role is to keep the traffic moving smoothly. And what an incredible variety of transport there is. Wagons drawn by assorted beasts of burden - have you ever seen the centaurs at work? And you will see cars and trucks from the Mundane world fitted with supplementary motive power which works by Magic. These are usually tame daemons, although I'm personally not convinced that the beasts are ever really domesticated.