Originally from DG PB p.885
quote:
[Said by Duiker to Mallick Rel, I think]. . . Aren's walls are high, well impregnated these days with Otataral, I believe - proof against sorcery. . .
Now this suggest to me that it was done pretty recently or at least in the Malazan Empire era. Maybe it always Otataral present but the malazan heavily reinforced it after conquering Seven Cities

