A´LSIUM(Ἄλσιον: Alsiensis: Palo), a city on the coast of Etruria, between Pyrgi and Fregenae, at the distance of 18 miles from the Portus Augusti (Porto) at the mouth of the Tiber. (Itin. Ant. p.301.) Its name is mentioned by Dionysius (Dionys. 1.20) among the cities which were founded by the Pelasgians in connection with the aborigines, and afterwards wrested from them by the Tyrrhenians (Etruscans). But no mention of it occurs in history as an Etruscan city, or during the wars of that people with Rome. In B.C. 245 a Roman colony was established there, which was placed on the same footing with the other coloniae maritimae;and in common with these claimed exemption from all military service, a claim which was, however, overruled during the exigencies of the Second Punic War. (Vellei. 1.14; Liv. 27.38.) No subsequent notice of it occurs in history, but its name is mentioned by Strabo, Pliny, and Ptolemy, and we learn from an inscription of the time of Caracalla that it still retained its colonial rank, and corresponding municipal organisation. (Strab. pp. 225, 226; Plin. Nat. 3.5. s. 8; Ptol. 3.1.4; Gruter, Inscr. p. 271. 3.) It appears to have early become a favourite resort with the wealthy Romans as a place of retirement and pleasure ( maritimus et voluptarius locus: Fronto, Ep. p. 207, ed. Rom.); thus we find that Pompey the Great had a villa there, and Caesar also, where he landed on his return from Africa, and at which all the nobles of Rome hastened to greet him. (Cic. pro Milon.20, ad Fam. 9.6, ad Att. 13.50.) Another is mentioned as belonging to Verginius Rufus, the guardian of Pliny, and we learn from Fronto that the emperor M. Aurelius had a villa there, to which several of his epistles are addressed. (Plin. Ep. 6.10; Fronto, Ep. p. 205—215.) At a later period the town itself had fallen into utter decay, but the site was still occupied by villas, as well as that of the neighbouring Pyrgi. (Rutil. Itin. 1.223.)
The site of Alsium is clearly fixed by the distance from Porto, at the modern village of Palo, a poor place with a fort and mole of the 17th century, in the construction of which many ancient materials have been used. Besides these, the whole shore to the E. of the village, for the space of more than a mile, is occupied by the remains of buildings which appear to have belonged to a Roman villa of imperial date, and of the most magnificent scale and style of construction. These ruins are described in detail by Nibby ( Dintorni di Roma, vol. iii. pp. 527, 528).
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