Accusative of Extent
In addition to its job marking direct objects of verbs and objects for most prepositions, the accusative case can also show extent of time or space.
In silvā trē s horā
It is worth noting that English requires the preposition “for” while Latin uses none at all. In fact, the accusative and ablative case uses discussed in this chapter require prepositions in English, though not always in Latin.
The smallest unit of time in the Roman world was the hour (hō ra). The amount of time from sunrise to sunset was divided into twelfths using a sundial. An hour, then, was one-twelfth of the day. In the winter when days were short, so were the hours. In the summer the opposite was true. Nighttime was divided into four vigils (vigiliae). The end of the first vigil and the beginning of the second came when whatever constellation had been on the eastern horizon at sunset made it halfway up to the zenith.