Hungary started building a fence on Monday along its border with Serbia to try to stop illegal migrants entering from the south, a barrier which German Chancellor Angela Merkel has said makes "no sense". Tens of thousands of migrants, mainly from the Middle East and Africa, use the Balkans route to get into the European Union, passing from Greece to Macedonia and Serbia and then to the EU's visa-free Schengen zone that starts in Hungary. Hungary has registered more than 70,000 migrants so far this year, compared with 43,000 in the whole of last year.