Good point on the nymph. We could substitute a geni locii (spelling?). The spirit of the river or perhaps of a spring that feeds into it.
Wouldn't the genius loci of a river want to be unchained from the bond of a dam? That might prove a difficult to grant, becauae of the resulting interference with mumdanes... It might instead be that of the resulting lake. Or of the mountain itself.
When I read the write up,I think I assumed the dam and aqueduct had fallen into pieces before the start of the saga date. Didn't occur to me the dam could still exist in the 1200s. That's what I get for assuming... 
Nymph would work. She is already there suposedly.
I actually made the reverse assumption, that the Roman aqueduct and dam were still in use in the 1200s. I don't have any solid info either way. But to thrive, cities need water. And the city is described as doing well, so either the aqueduct is still operational, or the city made some other change to make sure it gets enough water at all times.
A nymph leave me relatively indifferent, but it isn't that important to me as a player.
While looking for some details about the Roman aquaduct of Patras (I didn't find much), I stumbled upon another great potential site for the covenant about 30 miles (50 km) east from that city.
Boura (also Bura, Bira; Greek: Βοῦρα) was an ancient city of Achaea, Greece, one of the 12 cities of the Achaean League. It is said to have derived its name from Bura, a daughter of Ion and Helice. Strabo relates that there was a fountain at Boura called "Sybaris", from which the river and city in Italy derived its name. A little to the east of Boura was the river Buraïcus; and on the banks of this river, between Boura and the sea, was an oracular cavern of Heracles surnamed Buraicus. The ruins of Boura have been discovered nearly midway between the rivers of Bokhusia (Cerynites), and of Kalavryta (Buraicus) near Trupia (this is very close to the modern-day village of Mamousia).
Close to Mamousia, the Buraïcus river passes through dense vegetation and tunnels with many caves, passes and crags. This would be a great place for vis sources, as would the ruins of Boura and the oracular cave. The lands surrounding Mamousia are a great place to raise sheep and goats, as well as raise foodstuff for the covenant. The labs could be in the ruins as well.
Mamousia (which didn't exist at the time) is only 4 miles (6 km) from the coast, and the town of Vostitsa (mordern-day Aigio) is only 10 miles (16 km) away. The town was the seat of the Barony of Vostitsa. The barony, established in 1209 with eight knight's fiefs attached to it, was given to Hugh I of Charpigny and is part of the Principality of Achaea just like Patras. This is just far enough to give the covenant some breathing space with the mundane nobility, yet close enough for us to benefit from the ease of travel.
There would be multiple possibilities for a patron: genius loci of the Baraicus river gorge, a magical spirit haunting the ruins of Bura, an oracular spirit in the cave, or a magical creature inhabiting the river gorge.
Regarding the Romanos aqueduct, I like the idea of a nymph who was formerly worshiped as a deity and is now protective of whatever is left of the aqueduct because it reminds her of those days. If the aqueduct is still supplying the city with water, she might be angry that people are still using 'her' aqueduct but not giving her the proper respect. It's easy to imagine such a nymph allying herself with magi who are prepared, if not to revive her pagan worship, at least to pay her some attention.
It also gives me an idea for a possible companion character: a faerie-blooded descendant of the nymph, who is unaware of her heritage but finds herself inexplicably drawn to the area.
I'm not too attached to either idea if the group wants to go for something different, though.
Keep in mind that faerie and magical characters are possible, though if it is going to be the covenant patron it should probably be either a companion or mythic companion...
I also thought I wrote a post about the fact that, from a Byzantine perspective the Roman Empire lived on in the Byzantine Empire, and as such it only fell in 1204, and I would presume then that the aquaducts would still be in good working order, and also that they were constructed during the pagan Roman times and thus have been built in a way that would not disrupt any faerie or magical auras.
I don't yet have a companion idea I'm attached to, so if the group wants the patron to be a PC and likes the idea of the aqueduct-nymph, I'd be happy to play her as a companion/mythic companion level character. Since she would be the covenant patron I think I should wait to see what the rest of the group thinks, though.
From the point of view of a faerie deity, I'd imagine that the Roman Empire fell when it switched from pagan worship to Christianity!
Although that gives me another companion character idea: a child born in 1204 would be sixteen when the saga starts, which is a reasonable age for a non-magus starting character. Perhaps a supernatural character whose birth was linked to death of the Roman Empire? I don't think this is one I'd want to play, but maybe it's an idea someone else could take if they're stuck.
Some notes about Patras, in case they are helpful:
Well, Patras for certain has a history about it.
I know of the Roman Odeum, but never have heard about the aqueduct (which
now I know of since you mentioned it:
elabs.dreamhosters.com/achae ... -attractio
ns/245-bridgeaquaduct)
Now, what kind of features would you like? I mean natural features are of
course the mountain range that spans Patras in parallel (Mount Panachaikon).
Actually I don't think I know more than what is written in
en.wikipedia.org/wiki/Patras
To summarize for you info in these pages that I know of are:
- Roman Odeum
- Mount Panachaikon
- Patras Castle
- Roman bridge over river Milichos (exists in northern suburbs of Patras)
Now, info you'll not find in the wiki is:
From the Patras harbor across the Corinthian gulf are two well-known
mountains Varasova and Palaiovouna (old mountain).
In addition across the Corinthian gulf there is the city of Nafpaktos (seen
from Patras). Nafpaktos is also a very old town and certainly existed before
800 years (actually has 3500 years of history).
(nafpaktos.gr/culture/history-of-nafpaktos/)
I think that in very clear days, maybe the lake of Mesollogi can also be
seen but I'm not certain.
Also of potential interest is the fact that the area is apparently prone to earthquakes.
I was planning to use that as a surprise...
Sorry to spoil it. Read that and went "story!"
No surprise about the earthquake themselves. I expected we will have to build the covenant to take them into account. Maximilian grew up in this region, so he would expect them to happen once in a while.
Okay, we have a location (mountain spring near Patra) which puts us inside the Ionian Phyle, with a patron of either a genus loci which has been worshiped as a nymph or an actual nymph. We should probably decide which it is, and the next question becomes whether we want a conscious space- where the covenant patron would be aware of disturbances throughout. We have decided on two income streams (scriptorium and shepherding), either as a free virtue of 2 lesser incomes or a minor virtue of secondary income, in which case they are 2 normal sources of income. If we choose any of thee boons (aside from free) we need to decide on hooks to go with them.
Aura is a default of 3 but can be changed with appropriate boons or hooks.
If our patron is a faerie nymph then we need to consider the possibility that we have a faerie aura (hook)
Our building is likely a manor house, and could either be stone (free) or wooden (minor hook)
There are all kinds of possibilities for both hooks and boons when it comes to covenfolk, which haven't been discussed beyond the fact that most are either professionals in book manufacture or else shepherds.
If we can afford it I think the major boon of exceptional book would fit well...
Patra is also the capital of the Principality of Achaia, so I suspect that some form of political involvement is likely, if not at the beginning then as an unknown hook or future development.
I like having an actual Nymph as our Patron, which would then give us the Faerie Aura/Regio Hook.
I'm also good with having the Manor House be Wooden, which gives us a couple of potential story arcs (probably due to inclement weather and needing to repair it afterwards) as well as giving us the chance to either change it out in-game by ourselves or hire someone in-game to fix it up for us. I also just like the how the words "she walks across the rickety wooden floor, the boards creaking in time with the wind slipping in through the cracks in the walls" just come right out. 
As far as covenfolk go, I'm not sure what boons/hooks could be done here. I'll have to look through my books and get back to you on that.
An exceptional book written in Greek could lead to some interesting stories. Magi from other tribunals might be willing to pay handsomely for a Latin translation of the book, while jealous Greek magi might want to prevent such a translation from being created.
I like the idea of the Nymph patron, and clearly we make sure she can pass through the Aegis of the Hearth we cast.
A wooden Manor house for now is fine.
I would like at least 2 minor boons for increased Aura (brining it to 5).
My only concern with the base Aura being of Faerie is that this would seem to cause all of us additional warping. Which seems very expensive. Am I misreading the warping rules? If it does cause warping, would it make sense to do it as a Faerie Regio inside our aura?
I am inclined to go with the minor income virtue giving us two normal incomes.
There ought to be enough other interesting minor hooks to be able to afford the exceptional Greek book, which I agree would be interesting.
I'd prefer the Faerie Regio within our Aura personally. A little getaway for our Nymph friend.
As for the exceptional book, my character is Milivi...so it could be a gift from his mother to the covenant to help get us started.
Faerie Aura would only cause warping if it were 6 or higher, a faerie regio (hook) within a magic aura could certainly work...
Personally, I see no reason for us to go with a Faerie aura. None of us are even close to a Merinita concept, so all it would bring are disadvantages. Warping would only be an issue if the aura's strength is 6 or above, but the problem is with botch dice whenever we want to cast spells. That includes casting of the Aegis, which is already risky enough because of the raw vis powering the ritual.
Now, having a Faerie regio for the patron would be fine. Or a magical regio for the covenant within the Faerie aura. Or simply having a magical water spirit (genius loci) instead of a faerie nymph. Any of these options would be fine to me.
One thing I have wondered is, do we want all of these magi packed into a single location? After all, strictly speaking, only the labs themselves need to be inside a magical aura. Well, perhaps some of the scriptorium activities also, if we want some of the books clarified (the magical empowerement of books in covenant).
Two income stream are fine to me. Are we going to go into much details about silver? There are rules in Covenants about that, but that can entail a lot of bookkeeping. And if we use them, you'll see that we will need two full sources of income, if only to maintain labs for 10 magi.
Looking at the hooks and boons, here what I would see us having:
- Aura (site, minor boon) to raise the aura to 4. Not essential, but would be nice.
- Healthy Feature (site, minor boon) from the magical spring's water. Again not essential but nice.
- Flickering Aura (minor site hook) might be taken with a twist -- if we don't undertake whatever task that is required, our magical aura is overcome by a Faerie one for the year. This might be because of the Regio hook below.
- Regio (site, minor hook) within which our patron resides. It could be a Faerie regio (and a Faerie patron).
- Manor House (fortification, free choice) which will be quite large if it is to house so many magi as well as the scriptorium operations. Or it will need to be multiple buildings.
- Wooden (fortification, minor hook) would be another reason to have multiple buildings, to prevent any catastrophe (such as a lab accident) from destroying large parts of the covenant.
- Secondary Income (ressources, minor boon) so that we have two normal sources of income. We will need it.
- Indebted (resources, minor hook) would make sense for a new covenant, as it is doubtful that these individual magi would have had enough ressources to build the covenant. This might be a vis debt, if we were sponsored by another covenant.
- Peasants (residents, free choice) as most of our covenfolk would be shepherds.
- Chapter House (residents, major hook) might be an option if we want to have a secondary site, such as Boura. There might be a valuable vis source there, such that we made sure to secure the site by always having at least one magus living there. Just a possibility.
- School (residents, major hook) would also be a possibility and help explain our success as a scriptorium as well as access to the lands we control. This might be a rather large problem since we have at least one maga with the Blatant Gift, although well-designed internal security (such as segregated parts of the covenant) might help a little with this.
- Exceptional Book (external relations, major boon) on some Art. Deciding which Art will may not be so simple, as we have a rather large variety of interests amongst the magi.
- Local Ally (external relations, minor boon) would be about our patron (see TSE p.30).