These are the huge buttresses in the centre of the picture.
It’s the Emperor Septimius-Severus who gave that grandiose
complex to the Palace, after a severe fire of the buildings in 191.
Actually the construction is the extension of the south-east angle
of the hill and demanded powerful arcades to sustain the whole building.
A belvedere offered a splendid sight over the Circus Maximus;
The Baths of Septimius-Severus
) were part of a complex close
to the Pulvinar, or imperial loggia in Domitian’s Stadium.
A closer view of the Baths. In the foreground the Septizodium.