Raša River
... that though the Raša River in Croatian Istria is less than 30 km (19 mi) long, it has formed a political boundary for much of the last two millennia?
... that though the <b id="mwF-8"><a class="mw-redirect" href="./Raša_River" id="mwF_A" rel="mw:WikiLink" title="Raša River">Raša River</a></b> in <a href="./Istria_County" id="mwF_E" rel="mw:WikiLink" title="Istria County">Croatian Istria</a> is less than <span about="#mwt64" data-mw='{"parts":[{"template":{"target":{"wt":"convert","href":"./Template:Convert"},"params":{"1":{"wt":"30"},"2":{"wt":"km"},"abbr":{"wt":"on"}},"i":0}}]}' id="mwF_I" typeof="mw:Transclusion">30</span><span about="#mwt64" typeof="mw:Entity"> </span><span about="#mwt64">km (19</span><span about="#mwt64" typeof="mw:Entity"> </span><span about="#mwt64">mi)</span> long, it has formed a political boundary for much of the last two millennia?