The preposition intrā takes an accusative. It is likely derived from the adjectival feminine adjective singular of inter, intra, intrum (intrā) — an archaic adjective which also produced the corresponding preposition inter.
Intra + accusative is primarily used with a single class of nouns, and denotes a space ‘within which.’
- intrā moenia, within the walls
- intrā me deus est, the Lord is within me
- intrā iactum telī, within a javelin’s throw (denoting distance)
Intra + accusative of time is one ways of denoting the time within something occurred.
- intrā quattuor annōs, within four years
- intrā lucem, before the day was done
- intrā diēs paucōs, within few days (before a few days had passed)
- intrā morae breve tempus, without a moment’s delay
It can also mean less than a given duration or quantity.
- intrā centum fūnera fēcit, he inflicted fewer than 100 casualties
- intrā trēs diēs abiit, he left before three days had passed (compare above)
It can also appear without a direct object.
- ea intrā est, she is within
The Essential AG: 130