The justification for this plaque is dubious. Islington Local  History Centre
has provided the following information:

‘An 1805 Dent map suggests remains of a roman camp around what was to
become the Hungerford Road area. Most historical texts suggest there were
fortifications in Highbury, Battle Bridge (King's Cross) and Barnsbury.
Highbury Hill might have been a summer camp, as its elevation might have
proved useful. However, that said, although the plaque is a genuine council
plaque it seems that the information used to justify it was a little questionable.
Mary Cosh, for instance, explains that the local "roman remains" have been
identified as medieval  and many of the theories of roman fortifications are
from texts from the eighteenth to mid-twentieth centuries.
Of the modern literature which does suggest roman activity in Islington I have
not found mention of it happening at where Hungerford Road now stands.’