900. The supine stem is formed by the suffix #-tu-#, which is often
changed to #-su-# (912).
This suffix is attached to a root or to a form of the present stem after
the manner of the perfect participle (906): as, #nūntiātum#, _to
report_, #nūntiātū#, _in reporting_, stem #nūntiātu-#. Many of the
commonest verbs have no supine: as, #sum#, #eō#, #ferō#; #regō#, #emō#,
#tegō#; #amō#, #dēleō#, #doceō#, &c., &c.