Roman writers on Agriculture attached considerable importance to the keeping of pigeons, not merely as an article of food but on account of the valuable manure they yielded. Their statements are borne out by numerous references in the Papyri. Pigeon-keeping in Egypt must have been exceedingly profitable. The price of a dead bird was an obol, a pair rears sixteen or more young ones per annum, and a pigeon-house might contain a thousand nests. The valuable manure, used especially for vineyards, would probably pay, or more than pay, for such food as the pigeons did not pick up for themselves. It is therefore not surprising that in Ptolemaic times a 33⅓% tax was imposed on profits, for which the Romans substituted a tax estimated according to the size of the dovecot.