The death toll rises but still they come.

In the space of the last few days, the Italian Coast Guard rescued 93 people off Sicily and the US Navy pulled more than 100 men from a raft in rough conditions off the coast of Malta.

But it was earlier this month that the true scale of the human cost of migration was brought home when a boat packed with more than 500 Eritrean men, women and children caught fire and capsized off the coast of Lampedusa in the Mediterranean Sea. Only 155 people survived, and 364 bodies have since been recovered.

Once considered the centre of the world and the cradle of European civilisation, the Mediterranean Sea has become a death trap for the thousands of refugees from Africa and the Middle East who dream of reaching a better life.

Crowded into makeshift boats with amateur crews these pitiful cargoes take to the sea more in hope than expectation and having handed over their life savings to sailors who are little more than pirates.

So far, an estimated 32,000 have chanced their luck this year but many get no further than the coastlines of the islands of Malta, Sicily or Lampedusa where their luck runs out. Migration charities believe that as many as 20,000 people have died at sea while trying to reach Europe in the last two decades, a dreadful statistic which forced Joseph Muscat, the prime minister of Malta, to call the surrounding Mediterranean a "cemetery" for desperate migrants.

Most come from the Horn of Africa or from north Africa and the Middle East, desperately trying to escape the ravages of civil war and giving up one set of dangers for another. Migration patterns change as wars break out, economies shift, and countries crack down.

This week we look at where these migrants come from and why. We examine, too, whether the time has come for concerted action.