Brescia - Duomo Vecchio

The "Duomo Vecchio" (aka "Concattedrale invernale di Santa Maria Assunta", "La Rotonda") is a large circular structure erected on the site of a prior basilica in the first half of the 11th century.
This basilica ("Santa Maria Maggiore") was built within the 6th century. When the relics of Saint Filastrio (aka "Saint Philastrius"), the 6th bishop of Brescia and a preacher against the Arians, were transferred to Brescia in 838, a large, still existing crypt was built under that basilica.

The inner diameter of "La Rotonda" is 19,80m.
The ambulatory around is 5,50m wide.

The presbytery was erected over the old crypt. It was completed in the late 15th century. Some glass windows are in the floor of the transept, as there are still parts of the former basilica Santa Maria Maggiore.

Here is a mosaic, depicting a flock of sheept, hat is probably 6th/7th. century.

Following the information given, the message is:

Syrus diac(onus) h(unc) l(ocum) t(essellavit) c(um) s(uis)

What translates to "Deacon Syrus and his family donated this place/mosaic"