Definition of "bartisan"

she soon found it had no communication with any other part of the battlements, being an isolated bartisan, or balcony, secured, as usual, by a parapet, with embrasures, at which a few archers might be stationed for defending the turret, and flanking with their shot the wall of the castle on that side.

1819 December 20 (indicated as 1820), Walter Scott, chapter X, in Ivanhoe; a Romance. […], volume II, Edinburgh: […] Archibald Constable and Co.; London: Hurst, Robinson, and Co. […], page 165

There were flambeaux on staggering poles every ten strides or so, and at intervals of about a hundred strides, bartizans whose guardroom windows glared like fireworks clung to the bridge piers.

1980, Gene Wolfe, chapter XIV, in The Shadow of the Torturer (The Book of the New Sun; 1), New York: Simon & Schuster, pages 131–132