Pumice

Pumice is an igneous rock derived from lava. It is light and porous. Pumice was used as a building stone by the Romans and has been much-used in making grottos because it favour the growth of plants.<a href="/history_theory/garden_books/ml_gothein_history_garden_art_design/greek_contact_eastern_gardens#pumice">Example 1: Greek contact with Eastern gardens</a>