Names of towns, and domus, home, and rus, country, have another case -the locative- expressing place where.
In singulars of the first and second declensions in the locative is like the genitive: Romae, at Rome.
In all others it is like the ablative:
Carthagine (Carthago, Carthaginis), at Carthage.
But rus, country, has ruri or rure, in the country.
See No. 915.