fortifying russian

• ока́пывающий

  entrenching, digging trenches, fortifying with earthworks

• укрепля́вший

  strengthening (having strengthened), fortifying (having fortified)

• укрепля́вшийся

  strengthening (itself), fortifying (itself), that was strengthening, that was fortifying

• укрепля́ющий

  strengthening, reinforcing, fortifying, consolidating

• упрочня́вший

  strengthening, reinforcing, fortifying