Choirs are positioned at the side, not in front of the altar.
But I’m just noting that what you’ve called “common” is something you really don’t have an idea about…
I don’t appreciate the ad hominem. The Ceremonial I am talking about is complete with diagrams of the different configurations. Choir stalls are alongside the walls, either ahead of, or behind the altar. Sometimes in a U shape.
When the stalls are behind the altar towards the apse, the altar is in on a centreline between the two rows of stalls. If the priest is at the altar, he may either be looking towards the choir stalls, or towards the nave, depending on his orientation. In one configuration he will celebrate facing the people, in the other, facing the clerics or religious in the stalls. Both are allowed and detailed in the rubrics.
Here’s an example:
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It’s the abbey church at Sant’ Anselmo in Rome (where I have stayed several times). The altar and sanctuary is between the stalls (the wooden structures either side) and the nave.
I have been to many monasteries in Europe, and to more than one cathedral. I have seen these arrangements with my own eyes. I’m not pulling this out of thin air.
Another example with the same arrangement, Douai abbey in England:
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Here we have the arrangement where the altar is near the apse and the choir between the sanctuary and nave:
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You can’t see the choir stalls on account of the columns, but they are alongside the walls between the altar and nave.
The abbey I’m associated with is also similarly arranged, but very modern:
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Lastly, the cathedral where our schola regularly sings:
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The choir is arranged in an U-shape around the altar, with the altar between the choir and the nave. This cathedral was built in the '50s to replace one destroyed by fire.
I’ll suggest that what matters is you’ve called something “common” but when asked how common it was, you really don’t know. Less than 1% of all Churches in North America (or the Americas in general)? That would be my guess.
So, no - not common.
Common enough to mention in the rubrics. Common enough to be found in many monasteries and cathedrals around the world. Please note that the Church is not limited to North America and the rubrics are for all.
I would also respectfully suggest, that you too, by your own admission, are
guessing that this applies to only 1% of churches so your guess at “uncommon” is as good as my guess of “not insignificant”. And even if your number were accurate, given that they’re usually cathedrals, basilicas or monasteries, they are very
prominent churches in the areas the are located and the cathedrals in particular, cover a large population basin.
They’re ancient churches and teach us something about liturgical tradition.
But they don’t preclude us from evolving our traditions in our own way. I don’t mean that their traditions are insignificant, but they are theirs.
So, people grow up with the EF and it forms their liturgical sensibility.
And people have grown up with the OF and it has formed their liturgical sensibilities. Blessed as I am to have a nearby OF in Gregorian chant done with monastic sensibility to the Liturgy, a monastery of the Solesmes congregation, I can appreciate that the OF has its own inherent beauty when done with care and love.