tanta iustitia dicitur...

In Orberg’s LLPSI Cap 37 scripsit:

Italiae incolae primi Aborigines fuerunt, quorum rex Saturnus tanta iustitia fuisse dicitur…

Orberg explains; tanta iustitia as the ablative of the feminine noun iustitia, -ae. He says ‘tanta iustitia’ = tan iustus esse.

OK so I understand what it means but what literally does it mean. Iustitia is a noun not an adjective… is this an ablative of means meaning something like ‘…whose king Saturnus is said to have [ruled] by or with justice…’? with ‘regno, regnare’ simply implied…?

tantâ justitiâ = so much/very just, I think “was [made] of/from so much justice” Ablative of Source or Material // Ablativum Materiae vel Causae ?

gratias tibi ago Adriane