Interior of the Pantheon, now the church of Santa Maria dei Martiri.

Phocas at the request of pope Boniface commanded in ueteri fano quod Pantheum uocabatur, ablatis idolatrie sordibus, eclesiam beate semper uirginis Marie et omnium martirum fieri, ut ubi quondam omnium non deorum, sed demoníorum cultus agebatur, ibi deinceps omnium fieret memoria sanctorum.

– Annals of Tigernach, T605.1

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Other sources date the transfer of the Pantheon to the Church to anno 609.

[A]fter the pagan filth was removed, a church should be made, to the holy virgin Mary and all the Martyrs, so that the commemoration of the Saints would take place henceforth where not gods but demons were formerly worshipped.

Pantheon exterior.