Here is the text of the letter from the CDWDS that I referenced in my previous post:
Congregation for Divine Worship and the Discipline of the Sacraments
Prot. No 2036/00/L
The Congregation for Divine Worship and the Discipline of the Sacraments has been asked whether the expression in no. 299 of the Instituto Generalis Missalis Romani constitutes a norm according to which, during the Eucharistic liturgy, the position of the priest versus absidem [facing towards the apse] is to be excluded.
The Congregation for Divine Worship and the Discipline of the Sacraments, after mature reflection and in light of liturgical precedents, responds:
Negative, and in accordance with the following explanation.
The explanation includes different elements which must be taken into account.
It is in the first place to be borne in mind that the word expedit does not constitute an obligation, but a suggestion that refers to the construction of the altar a pariete sejunctum [detached from the wall] and to the celebration versus populum [toward the people]. The clause ubi possibile sit [where it is possible] refers to different elements, as, for example, the topography of the place, the availability of space, the artistic value of the existing altar, the sensibility of the people participating in the celebrations in a particular church, etc. It reaffirms that the position toward the assembly seems more convenient inasmuch as it makes communication easier (Cf. the editorial in Notitiae 29  245-249), without excluding, however, the other possibility.
However, whatever may be the position of the celebrating priest, it is clear that the Eucharistic Sacrifice is offered to the one and triune God, and that the principal, eternal, and high priest is Jesus Christ, who acts through the ministry of the priest who visibly presides as His instrument. The liturgical assembly participates in the celebration in virtue of the common priesthood of the faithful which requires the ministry of the ordained priest to be exercised in the Eucharistic Synaxis. The physical position, especially with respect to the communication among the various members of the assembly, must be distinguished from the interior spiritual orientation of all. It would be a grave error to imagine that the principal orientation of the sacrificial action is [toward] the community. If the priest celebrates versus populum, which is a legitimate and often advisable, his spiritual attitude ought always to be versus Deum per Jesus Christum [toward God through Jesus Christ], as representative of the entire Church. The Church as well, which takes concrete form in the assembly which participates, is entirely turned versus Deum [towards God] as its first spiritual movement.
It appears that the ancient tradition, though not without exception, was that the celebrant and the praying community were turned versus orientem [toward the East], the direction from which the Light which is Christ comes. It is not unusual for ancient churches to be “oriented” so that the priest and the people were turned versus orientem during public prayer.
It may be that when there were problems of space, or of some other kind, the apse represented the East symbolically. Today the expression versus orientem often means versus apsidem, and in speaking of versus populum it is not the west but rather the community present that is meant.
In the ancient architecture of churches, the place of the Bishop or the celebrating priest was in the center of the apse where, seated and turned toward the community, the proclamation of the readings was listened to. Now this presidential place was not ascribed to the human person of the bishop or the priest, nor to his intellectual gifts and not even to his personal holiness, but to his role as an instrument of the invisible Pontiff, who is the Lord Jesus.
When it is a question of ancient churches, or of great artistic value, it is appropriate, moreover, to keep in mind civil legislation regarding changes or renovations. Adding another altar may not always be a worthy solution.
There is no need to give excessive importance to elements that have changed throughout the centuries. What always remains is the event celebrated in the liturgy: this is manifested through rites, signs, symbols and words that express various aspects of the mystery without, however, exhausting it, because it transcends them. Taking a rigid position and absolutizing it could become a rejection of some aspect of the truth which merits respect and acceptance.
Vatican City, 25 September 2000.
Signed: Jorge Arturo Cardinal Medina Estévez, Cardinal Prefect
Archbishop Francesco Pio Tamburrino, Archbishop Secretary
I hope this helps.