St. Irenaeus speaks of a certain number of letters written by Polycarp,[8] but we have only his letter to the Philipplans, written on the occasion of Ignatius' sojourn among them.
We have Polycarp's reply, written probably soon after the death of St. Ignatius,[9] but the entire text is extant only in a mediocre Latin translation. All the Greek manuscripts which have reached us stop towards the end of ch. ix. Fortunately Eusebius has transcribed the whole of ch. ix as well as ch. xiii, - the two most important chapters.[10]
The oldest collection of the writings of St. Ignatius known to have existed was that made use of by the historian Eusebius in the first half of the fourth century, but which unfortunately is no longer extant
http://www.earlychristianwritings.com/tixeront/section1-1.html#polycarp
Very good! :)