Let me start by saying I prefer the idea that most mature (Summer /Autumn ) Covenants should have a Mercere Portal or three that they control.
For all the usual reasons - emergency entrance during siege, access of secret stockpile, easy commute to friends and long term useful places, etc.
Part of the secret stockpile concept, includes access to agricultural farms making produce that can't be grown at the Covenant.
Wheat, grains, olive oil, even wine could count.
Where in an out-of the way place would you put your secret farm?
I am assuming it is in a reasonably fertile area, that doesn't have much risk of being pillaged and burnt by feuding armies on a semi regular basis.
Is there anywhere in Mythic Europe that might qualify ?
The alps. Before accurate scientific mapping was invented in the 1700s it was entirely normal for surveyors to miss large areas such a valleys that are hard to enter. If you have no accurate measurements of the land it is not possible to make a good map that will tell you that you have a gaping hole in the middle of the map and thus deduce that something is there.
This is fact could be generalized to any mountainous area in mythic europe. If you have a good valley but it can be found and entered normally you can seal of the entrance with magic after building your portal there so that the valley becomes hidden, after a few generations the mundanes will remember it only in legends.
The sahara is another good one. It is quite possible to go deep into the desert build a mercere portal and never get any visitors. You can then use magic to conjure rain to grow whatever you need. Bonus points for going into the mountains in the interior of the Sahara.
Then there are Regiones. If you can find a regio, preferrably one that is in an out-of-the-way location or just plain hard to enter then you can hide your secret farming operation there.
Similar to mountains, islands are another good place to hide a secret farming operation. Again magic is useful in terraforming the island to have space flat enough for farming or weather magic to make the climate hospitable enough.
In germany you might even be able to get away with hiding such a thing deep inside the forest. You just need to make sure that no one is ever seen coming and going.
I think the fundamental questions are what are the cost of mercere portals and why you assume a summer covenant would have one. My assumption is that the vast majority if not all Mercere portals are tied into the redcap network, s having one gives you access to quick communication and more than one makes you a mercere covenant and a hub of communication. In my world the Mercere will not make a portal into Novgorod as a safety concern (there are big scary monsters in Novgorod and we don't want to give them a back door into the redcap network). Fundamentally there are, by the books, less than one mercere magus per tribunal, and constructing a Mercere portal must be done at both ends simultaneously, requiring 2 mercere mages, The effect is level 65 and 2 devices must be enchanted (only one mage need do the enchanting) which means 2 seasons of work, where most magi will only contribute 1 season per year to such contract work- thus I would estimate the house adds 1 portal to its network every 3 years, which is a long ways from every summer covenant having a couple at least.
Well there was that guy who was writing his self insert fanfic a while back with his gary stu mage who made friends with everyone was member of every tribunal, head of a covenant in each tribunal and was making a network of portals connecting them all...
But yeah, I see functioning portals as 1 per tribunal .
A few more, maybe. Not a whole lot though.
Part of my problem is actually House Mercere itself. The more available portals are, the less relevant the ordinary redcap will be.
Redcaps have to visit every covenant, and a number of tribunals, by the books have more than one portal (indded the standard seems to be one portal from harco to a tribunal and then a few more branching out from that central location to reach the further points of the tribunal) there are numerous Mercere portals that were lost or destroyed during the Schism war, and portals may need to be built or replaced depending on growth or shifting politics within a tribunal.
Canonically there are a bunch in Durenmar. Almost certainly House Mercere would set them up on request, but keep in mind the cost is going to be more than the cost of making them. I think it would ring in around 100 pawns per portal once all is said and done (20 to open it, 13 for the enchant, plus however much for any linked triggers to control access, 2-3 seasons per portal, and then profits).
I mean, it's cheap compared to keeping a regular Hermes Portal up for any amount of time, but no covenant spends 200 pawns of vis casually.
If they followed Verditius guidelines that would put the price at 3 queens for a portal, but they have a lack of competition that Verditius does not have and more limited production capability. so I expect it would be higher. Maybe 5-10 queens per portal.
Wait, Verditus rates are 3p per 1p in the item. At a minimum a Mercere Portal is 33p, so at Verditus rates it would be 99p per portal. Note that the Verditus basically form a cartel to keep these pricing levels, Verditus charging less would probably get into a lot of trouble (though they'd sell more items, which is something they want to do as well).
Mercere doesn't have a cartel but they do have limited supply of magi capable of the job, so them charging effectively Verditus rates seems fine, and let's face it, something like 66p profit for what amounts to 3 seasons of work (2 seasons + travel) can set up a Mercere magus for a long time. Not even old magi will turn their nose up a 20p+ a season for their labor.
Well I listed some at the thread beginning.
But left out what I think is a rather important one - Prestige. Publically employing Portal Magi to install a Mercere Portal (even if the Order as a whole doesn't know where the end location is) is one way of saying "this Covenant is powerful enough to have a Mercere Portal installed".
Based on the rest of this thread, I may have underestimated costs involved. For some reason I expected that Portal building Mercere Magi all had the Mercurian Magic virtue, to help reduce Vis costs in the rituals involved.
I dont really think that it matters much that you underestimated the price. 100 pawns is not IMO a terrible price to pay for a portal. Most old covenants will eventually accumulate a store of 100 pawns. If a covenant has an average surplus of 1 vis/year then it will be able to afford a portal a mere 100 years after its founding. That is within the lifespan of the founding magi. Personally I dont think it unreasonable that older covenants can manage an annual vis surplus more in the 3-4 or beyond range, especially if they are saving up for a big project like a hermes portal.
However Mercurian magic only helps reduce the cost in casting the spell "Hermes portal" it does not reduce the cost of crafting the enchanted portal frame that casts the same spell.
@John_Prins you say that the Verditius "basically form a cartel" and you are right, however the more period appropriate term is "guild" and unlike in modern times a pricing cartel is widely perceived as the most legitimate way of doing business.
I've always worked off the idea that there are pretty much two big portal networks - one that connects Harco to every tribunal (for Mercere use only) and another that connects Durenmar to several highly prestigious covenants with a lot of money and influence to throw around (or who were owed a big favour by house Mercere at one point).
The main restriction is the availability and willingness of skilled gifted Mercere, rather than the actual price of the portal. I would also imagine the Mercere aren't building portals for just any covenant with the vis on hand either - in theory some canny magus could commission a portal for their covenant and study it to try and learn how to make their own, which I doubt the Mercere would like. So only "trustworthy" covenants with long pedigrees and good relations with Harco get the privilege.
So this ends up around 1-3 portals per tribunal (not including the hubs in Harco and Durenmar). The Domus Magnae are connected, some very prestigious other covenants, most mercer houses, and there are a few extra sets off the main grid (ims we had a 6 portal loop connecting Verdi, Venice, and Ingasia, for example).
Of course this is just how I've done it in my sagas, but I think the portals are most interestingly if they are relatively rare as it increases the importance of the "famous" covenants and creates reasons to travel to them.
You make an interesting point in saying that the primary price of a portal is not so much the vis they cost but the prestige required to get house Mercere to agree to build a portal.
There's almost certainly periods when the House simply can't make portals due to a lack of skilled magi. Merceres lean towards Muto and Creo, not Rego Terram, and I imagine there are periods of decades where there simply are not any magi in the House capable of managing it. It really depends on how hard the House works to keep such magi in existence; for example, House Mercere might have legendary quality Rego and Terram books (L20 Q15) to encourage the gifted Merceres to study these arts, but even Re20 Te20 isn't enough to hit Lab Total of 65 (though with Magic Theory 10 they're only 15 points off, which is manageable).
Now whether or not House Mercere admits they have a capacity issue is another subject. Are covenants being stonewalled by House Mercere because there's a capacity issue? All the vis in the world isn't enough if they can't do it, but the covenant might feel it's being stonewalled because the primus doesn't like them.
It requires two magi working in concert to build a mercere portal, one at each location. One who invests the devices requires much more ability than the other.
If this doesn't scream master and apprentice I don't know what does. Considering how few Gifted Mercer there are assuming there is one portal aster at a given time who only creates portals when they have an apprentice (or ex apprentice assisting, possibly in exchange for further training) they may only be able to install portals for 45 out of every 125 years (rough estimation, depends how much study they would undergo after the retirement of the old portal master before they took an apprentice and set up shop) , which also means that they could (as a monopoly) set whatever prices they wanted for out of network portals.
I agree that this is a master-apprentice type scenario. Ideally it would be a 3 man situation (3 generations), 2 that are capable, with the oldest preparing the next successor. That way you could likely avoid gap-years (decades) in capability.
This was the set up of my Mercere Craft Magus, he was the 'new guy', while 2 older magi were doing the actual portal work while he worked on his arts.