We all know that during the 4th century the emperor Constantine constructed a Roman basilica over the grave of St. Peter. This was replaced during the renaissance with the current structure, as the old church had become structurally unsound during the interval.
A reconstruction of the old church, drawn in 1891, is here:
It would be interesting to know the authorities on which this drawing was based. Are there, indeed, old sketches of the basilica? There surely ought to be! And it was a Roman basilica, preserved intact, so should be of interest to classicists.