A balustrade is a row of repeating balusters - small posts that support the upper rail of a railing. Staircases and porches often have balustrades.
ballustrad, ballustrade, balluster
"The galleries were full of fashionably dressed ladies, leaning over the balustrade and trying not to lose a single word of what was being said below...."
Anna Karenin by Leo Tolstoy, Chapter XXX, Part VI. 1917.