The protection of an island location is almost equalled in the peninsulas formed by the serpentines or meanders of a river.  Hence these are choice sites for fortress or settlement in primitive communities, where hostilities are always imminent and rivers the sole means of communication.  The defensive works of the mound-builders in great numbers occupied such river peninsulas.  The neck of the loop was fortified by a single or double line of ditch and earthen wall, constructed from bank to bank of the encircling stream.[722] This was exactly the location of Vesontio, now Besancon, once the ancient stronghold of the Sequani in eastern Gaul.  It was situated in a loop of the Dubis, so nearly a circle that its course seems to have been “described by a compass,” Caesar says, while fortifications across the isthmus made the position of the town almost impregnable.[723] Verona, lying at the exit of the great martial highway of the Brenner Pass, occupies just such a loop of the Adige, as does Capua on the Volturno, and Berne on the Aare.  Shrewsbury, in the Middle Ages an important military point for the preservation of order on the marches of Wales, is almost encircled by the River Severn, while a castle on the neck of the peninsula completes the defense on the land side.[724] Graaf Reinett, at one time an exposed frontier settlement of the Dutch in Cape Colony, had a natural moat around it in the Sunday River, which here describes three-fourths of a circle.

[Sidenote:  River islands as sites of trading posts and colonies.]

The need of protection felt by all colonists in new countries amid savage or barbarous people whom encroachment sooner or later makes hostile, leads them if possible to place their first trading posts and settlements on river islands, especially at the mouth of the streams, where a delta often affords the site required, and where the junction of ocean and river highway offers the best facilities for trade.  A river island fixed the location of the English settlement at Jamestown in Virginia, the French at Montreal and New Orleans, the Dutch at Manhattan and Van Renssellaer Island in the Hudson, the Swedes at Tinicum Island in the Delaware River a few miles below the mouth of the Schuylkill.[725] St. Louis, located on a delta island of the Senegal River, is one of the oldest European towns in West Africa;[726] and Bathurst, founded in 1618 on a similar site at the mouth of the Gambia, has for centuries now been the safe outlet for the trade of this stream.[727] Such island settlements at river mouths are a phenomenon of the outer edge of every coastal region; but inland stations for trade or military control also seek the protection of an island site.  The Russians in the seventeenth century secured their downstream conquest of the Amur by a succession of river island forts,[728] which recall Colonel Byrd’s early frontier post on an island in the Holston River, and George Rogers Clark’s military stockade on Corn Island in the Ohio, which became the nucleus of the later city of Louisville.