After the loss of the Palantír of Osgiliath, and the capture of the Ithil Stone by the Dark Lord, the Lords of The Southern Kingdom were in want of a means of summoning the aid of Rohan in times of desperate need. So it was that the Beacons of the North were conceived and constructed along the line of the Ered Nimrais.
Built atop the best vantage points from Minus Tirith to the borders of Rohan, these were no ordinary pyres heaped for the amusement and warmth of revelers on days of celebration. Need dictated that they must be large and bright enough to pierce even the heaviest of mountain storms, and all but the thickest of mists, penetrating to the eyes of the Wardens who were posted to keep vigil and light their own beacons in turn.
In form they resembled great round barns, such as might be used to house cattle or keep store of grain. Their foundations were laid of stone, tall as a large man, wide as a great draft horse, twenty five yards from one edge to the opposite side. Like the spokes of a great wheel they spread out from the central post, forming wedge shaped gaps to permit the inflow of air. Atop these footings were constructed wooden frameworks of square hewn timbers cut from the boles of enormous oaks, pegged together with wooden pins and forming a circular wall the height of three men. The roofs then sloped upward towards central peaks, fully twenty yards above the top of the foundations, and the structures were clad in oak planking, thus protecting the fuel within from the elements.
Inside, a large grid of heavy iron bars lay atop the stones of the foundations, and were overlaid with planking of more seasoned oak, laid loosely with many gaps between. The whole of the inside of this space was filled with pieces of oak, beech and elm, cut and split, each faggot coated along its length with pitch, and laid in criss-cross fashion to leave space between each. On one wall of the structures were fashioned two large doors that could be swung open to allow men to bring in fuel to fill the interior, up earthen ramps from ground level. From those doors to the center of the piles of dry tinder, narrow corridors were formed leading to small chambers in the midst of the beacons. Here were stacked quantities of wood more finely cut than the rest and mixed with dry straw. Near at hand were kept large ewers of oil, to be poured upon the wood and aid the lighting of the fire.
Thus were the great signal lights of Gondor erected as buildings to keep all inside dry and quick to burn, while they themselves perished in the consuming fire. Being covered in pitch, the tinder within would belch forth great clouds of black smoke to be seen from a great distance during the day, and put forth a fury of flame and light that could be seen at great distance after the coming of nightfall. Once lit, even the heaviest of downpours could not quench the inferno and left alone, could burn unreplenished for more than a full day.
Such impressive hoards of fuel needed protection from unwanted sparks and bolts of lightning as often struck out from the terrible storms of the high peaks. Long ago, the engineers of the King had discovered that laying thick strips of copper on the tops of wooden halls and running them down into the earth would guard them from these perils. As an extra measure of protection, deep cisterns were carved into the rocky ground near at hand and filled with rain water collected by gutters of copper running round the eaves of the buildings. The Wardens of the Beacons could then endeavor to quench the flames with buckets and helms. In the event that a new beacon needed to be constructed quickly, this water would also serve to cool the ashes of the ruined hall to allow the work to proceed apace.
Not too great a distance from each Beacon were an assortment of smaller stone workshops and storage sheds. Here were kept the complete frameworks of new beacons, ready to be erected in a few short days after the old ones had been consumed. As well, enough store of dry wood was contained within to replenish what had been used and scores of jars full of pitch waited to be poured.
Early in their history, the Beacons of Gondor were kept manned by seldom fewer than four score of men apiece. These were housed in lodges amongst the trees a little ways down from the summits. The greatest number were Men of arms, posted there to protect both the wardens and the lights themselves from attacks, and lend aid in dousing unplanned fires. Carpenters were sent at whiles to keep the structures in good repair, and masons as well, to maintain the foundations and tend the other buildings. The Watch wardens were charged with the task of keeping constant vigil both night and day on the fires of the other heights so that they might act without delay in the lighting of their own. Only the Wardens of Amon Din were free of this chore, being instructed to light the fire only by the messenger of the Lord of the city.
As the years passed, the might of Gondor waned and was drawn ever more towards the eastern peril, causing the Rulers of the Southern Kingdom to send fewer and fewer to man and maintain the Beacons. By the time of Denethor II, fewer than fifteen at a time could be counted at those closest to Rohan, and of these, most were men of long service. At Amon Din, Eilenach and Nardol could be found no more than six or eight of the oldest still fit to serve. The Beacon at Nardol had come dangerously close to going up in flames in the fifth year of the rule of Ecthelion II due to a lapse of vigilance and was only just saved in time by the buckets of the Wardens before causing the whole of the signal line to be lit and destroyed without need. For a while the line was bolstered with greater manpower but need elsewhere once again put an end to this. After the last defeat of the great enemy, many felt that the Palantír of Minus Anor had played a major role in this policy of neglect, owing to The Lord Denethors growing dependence on the visions of the stone and the incomplete views that were directed his way.