
I have ended up writing more about Eregion again: specifically its fall, in Speak Friend and Enter. And I have another Second Age Eregion work slowly underway.
To help with all of this, I made a map of Eregion, aiming for the period around 1600 when the Ring was forged.
Here's the thinking behind it:
Eregion is largely a wooded landscape. Some of the trees have been felled to build the city of Ost-in-Edhil, and to provide fuel, but I think the woods would be preserved. Celeborn and his people came with Galadriel to establish Eregion, bringing Doriathrin forest agriculture skills with them.
Perhaps Galadriel has even tried planting mallorn trees here, though they did not take as well as they did in Lorien later, and vanished when there were no longer Elves in Eregion to look after them. The woods would be a source of materials, fuel, and bark, but also a place where the Elves would hunt, particularly deer.
At the end of the Third Age, when the Fellowship walked through Eregion, they noticed ancient remains, paved roads and worked stones. I am inclined to think some of these may have been Numenorean remnants from the early Third Age, rather than remains of Eregion, simply because of the 4760 years between the Fall of Eregion and the War of the Ring. Eregion/Hollin doesn't seem to be mentioned as being part of Arnor, but it is quite close to the Numenorean settlement of Tharbad.
(On the other hand, Eregion did specialise in the technologies of preservation, if the Rings are anything to go by. Still, a nearly 5000 year old road still recognisable as such tests my imagination somewhat.)
I am not sure if Elvish Eregion would have had the wide paved roads mentioned in Lord of the Rings. I think the roads I have marked on the map above were probably green roads, used for walking routes, occasional horse riders, and perhaps livestock droving, and that the paved roads may have come later.
Of course, the paved leading to Khazad-dûm with its wide climbing loops as described in LOTR, may have been a dwarf-road. The creation of loops to reduce the climb suggests that perhaps it was designed for use by heavy carts. There is no wide lake before the Doors, of course. That was created by damming the Gatestream, Sirannon, some time in the late Third Age.
At any rate. Tharbad does exist in 1600SA, but it's fairly new, and primarily a fort defending Numenorean timber extraction operations: there's no bridge yet, and the bogs and marshes along the line of the Swanfleet river are wide and shallow, with several small islands.
This land will all be drained later, either by Numenor, or perhaps by the new powers of Arnor and Gondor, building the road through Tharbad to connect Northkingdom and Southkingdom. But not yet. The forests that used to lie around the river Gwathlo have mostly been felled by Numenor, but there are some left, and most of those will be burned during Sauron's campaign.
I've given Celeborn a house outside Ost-in-Edhil. Given his well-documented distrust of Dwarves, I feel that he probably wouldn't be very comfortable in the city with the greatest friendship ever known between Dwarves and Elves. Also, during the fall of Eregion, Celeborn was present and joined Elrond's rescue force that was swept away into the north, to found Rivendell, and that would be more likely if Celeborn's usual haunts were at the northern end of Eregion. I've drawn his house with two long wings and a tower, and I'm inclined to think that the tower was Galadriel's idea, and was made of stone, but the wings were made of carven wood. There are other settlements scattered across northern Eregion through the woods, but no cities of any size: these are homes for Elves to use particularly in winter.
When the Fellowship stopped on the road from the Redhorn Gate, they stopped at a hill topped by a few trees, and ringed with large rocks. I've decided this was probably a way-meet, where two paths originally passed, and the trees are distant descendents of those planted by the Elves. The rocks might be remnants of late fortifications from the siege, perhaps linked to real-world myths about crossroads and waymeets.
The wide shallow bird-haunted Swanfleet is probably a useful food source for Tharbad, as well as the elves of southern Eregion and the Men of the great woods of Eriador. All of them hunt in the marshes for birds and eggs.
I think perhaps the Numenoreans of Tharbad (they all call themselves Numenorean, though even at this early date, some of them have never seen Numenor) mostly hunt on land, in the reedbeds. They are more comfortable with deep water ships than small boats.
The Elves of Eregion make long shallow punts that are driven with paddles or long poles, which allows them to hunt birds in season on the water with bows or falcons.
The marshes are also grazing land for cattle, the herds of the original inhabitants of the land along the Gwathlo river. They have been here for a very long time, long before Eregion was established, trading cheese, milk and leather with the dwarves of Khazad-dûm in return for metal: mostly in the form of knives, pots, pans and needles.