jats:titleAbstract</jats:title> jats:pThe infra-red limit of a planar static D3-brane in AdSjats:inline-formula <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="aab5eabieqn001.gif" xlink:type="simple" /> </jats:inline-formula> is a tensionless D3-brane at the anti-de Sitter horizon with dynamics governed by a strong-field limit of the Dirac–Born–Infeld action, analogous to that found from the Born–Infeld action by Bialynicki-Birula. As in that case, the field equations are those of an interacting 4D conformal invariant field theory with an jats:inline-formula <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="aab5eabieqn002.gif" xlink:type="simple" /> </jats:inline-formula> electromagnetic duality invariance, but the D3-brane origin makes these properties manifest. We also find an jats:inline-formula <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="aab5eabieqn003.gif" xlink:type="simple" /> </jats:inline-formula>-invariant action for these equations.</jats:p>