Borrell's military career seems to have been undistinguished — he is recorded as fighting only two battles and seems to have lost both - and it was under his rule that Barcelona was sacked in 985 by the Muslim leader Almanzor.
Karier militer Borrell tampaknya tidak berbeda - ia tercatat hanya berjuang dua pertempuran dan tampaknya telah kehilangan keduanya - dan itu di bawah pemerintahannya bahwa Barcelona dipecat pada tahun 985 oleh pemimpin Muslim Almanzor.