What does Ostiensis mean?

Latin Learning Latin
1

In Chapter XVI of LLPSI (Line: 26) Orberg gives us:

Portus Ostiensis semper plenus est hominum qui in alias terras navigate volunt.

Orbeg explains ‘Ostiensis’ in the margin as follows: Ostiensis-e < Ostia.

I don’t understand this. Is Ostiensis gen of Ostia?!

2

Ostiensis is the adjective derived from Ostia just as Romanus is the adjective derived from Rome; so it means of Ostia, or from Ostia.

Hope this helps.

Ingrid