What are those vessels on the Altar?

In all of the many pics, of the EF celebrated, on the feast of the Exaltation of the Holy Cross. I have noticed what seem like reliquaries, on the Altar between the canlesticks…

I attend the EF exclusively in my home parish, But I have never seen reliquaries, (if thats what they are) placed on the Altar.
Were these put there for the feast? And if so, do they contain pieces of the true cross? In honor of the feast?

I noticed them in the Mass from EWTN, And in pics from St. john Cantius, as well as the mass from the seminary in St. Louis…and many more, from Churches worldwide celebrating the EF on this day…
does anyone know?

Yes they are relics, from my understanding they are allowed on the altar during solemn Mass’ and Feasts

Thank you,Christopher!
I was certain thats what they were, Incredibly inspiring. The very bones of the Saints, attending the Holy Sacrifice.
God Bless

Most churchs still have an Altar Cavity that contains a Relic in the altar even in todays “Ordinary” parish’s

the older churchs have the Altar Stone that contains relics as well - they used to be REQUIRED for concecration

See:

newadvent.org/cathen/01351d.htm

Reliquaries may be on the altar for any Mass, not just Solemn Mass. They may not be on the altar during Exposition.

The tradition of having relics interred in the Altar comes from a practice in the early Church of building the Altar over the tombs of saints and martyrs. One of the symbolic functions of the Altar is a tomb.

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