E's ‘unam’ is the reading favoured by all modern editors. Either reading is possible in terms of sense and metre, and the choice is not an easy one. The attraction of ‘ unam’ is obvious and consists in the stress which it lays on Jocasta's isolation and vulnerability in the face of ‘omnis… iuuentus’. The appeal of ‘una’ is a little more subtle. It emphasises the coming together of the youth, whether Argive or Theban, in common cause against the aged Jocasta. It is ironical that the two fiercely opposed sides are urged to come together not against a mutual foe but against a defenceless old woman. And even more ironical is the notion of the brothers' uniting to kill their mother: from the beginning of the play they have been portrayed as uncompromisingly hostile to each other; now, bent on the impious act of fratricide, they are envisaged as acting together for the first time, but only to accomplish an equally great or even greater impiety – matricide. The reading of A is attractive not only because of the characteristic irony which it expresses, but also because it heralds the even stronger expression of the same notion in 445 with ‘ciuis atque hostis simul…’. One may note also that ‘omnis ruat / una’ appears to be an echo of Vergil's ‘una omnes mere’ (Aen. 8.689).