Already fossilized as early as Proto-Italic as po- in words like poner.
From Proto-Indo-European *h2p-o 'id.' From the full grade *h2epo "away" (see ab-)
Indo-European: Germanic: Old High German fane "from," Old Frisian fan 'id.,' Old Saxon fan 'id.' (h2p-o-neh2); Balto-Slavic *po: Old Church Slavonic po "after," "by," Russian po 'id.,' Czech po 'id.,' Bulgarian po 'id.' Lithuanian po-, a perfective-forming prefix. Balto-Slavic *pa: Old Church Slavonic pa, particle forming the perfective, Russian pa-, a perfective-forming prefix, Czech pa- 'id.,' Bulgarian pa- 'id.' Lithuanian pa- 'id.'; Albanian *apo: pa "without"