Charles H. Spurgeon on Psalms 129:6

Grass upon the housetops. In the morning the master of the house laid in a stock of earth, which was carried up, and spread evenly on the top of the house, which is flat. The whole roof is thus formed of mere earth, laid on and rolled hard and flat. On the top of every house is a large stone roller, for the purpose of hardening and flattening this layer of rude soil, so that the rain may not penetrate; but upon this surface, as may be supposed, grass and weeds grow freely, but never come to maturity. It is to such grass the Psalmist alludes as useless and bad. —William Jowett, in "Christian Researches in Syria and the Holy Land", 1825.