ĂRŪRA (ἄρουρα), a Greek measure of surface, mentioned by Herodotus, who says that it is a hundred Egyptian cubits in every direction. Now the Egyptian cubit contained nearly 17¾ inches; therefore the square of 100 by 17¾ inches, _i.e._ nearly 148 feet, gives the number of square feet (English) in the arura, viz. 21,904. ĂRUSPEX. [HARUSPEX.] ARVĀLES FRĀTRES, formed a college or company of twelve priests, and were so called from offering public sacrifices for the fertility of the fields. That they were of extreme antiquity is proved by the legend which refers their institution to Romulus, of whom it is said, that when his nurse Acca Laurentia lost one of her twelve sons, he allowed himself to be adopted by her in his place, and called himself and the remaining eleven “Fratres Arvales.” We also find a college called the Sodales Titii, and as the latter were confessedly of Sabine origin, and instituted for the purpose of keeping up the Sabine religious rites, it is probable that these colleges corresponded one to the other--the Fratres Arvales being connected with the Latin, and the Sodales Titii with the Sabine element of the Roman state. The office of the fratres arvales was for life, and was not taken away even from an exile or captive. One of their annual duties was to celebrate a three days’ festival in honour of Dea Dia, supposed to be Ceres, sometimes held on the 17th, 19th, and 20th, sometimes on the 27th, 29th, and 30th of May. But besides this festival of the Dea Dia, the fratres arvales were required on various occasions, under the emperors, to make vows and offer up thanksgivings. Under Tiberius, the Fratres Arvales performed sacrifices called the _Ambarvalia_, at various places on the borders of the ager Romanus, or original territory of Rome; and it is probable that this was a custom handed down from time immemorial, and, moreover, that it was a duty of the priesthood to invoke a blessing on the whole territory of Rome. There were also the private _ambarvalia_, which were so called from the victim (_hostia ambarvalis_) that was slain on the occasion being led three times round the corn-fields, before the sickle was put to the corn. This victim was accompanied by a crowd of merry-makers, the reapers and farm-servants dancing and singing, as they marched, the praises of Ceres, and praying for her favour and presence, while they offered her the libations of milk, honey, and wine. This ceremony was also called a _lustratio_, or purification. ARX signifies a height within the walls of a city, upon which a citadel was built, and thus came to be applied to the citadel itself. Thus one of the summits of the Capitoline hill at Rome is called _Arx_. The _Arx_ was the regular place at Rome for taking the auspices, and was hence likewise called _auguraculum_; or, more probably, the auguraculum was a place in the Arx. AS, or _Libra_, a pound, the unit of weight among the Romans. [LIBRA.]