Migration movements are rarely smooth.
People who are migrating have to negotiate a number of barriers when moving between countries.
A number of obstacles can get in the way such as legal restrictions, family attachments, and costs incurred etc.
Documentation is required to allow migration. Within the European Union (EU) migrants only need a passport. However, to migrate into other countries long application processes for visas or work permits are necessary.
Each country will have a specific set of rules about how many visas they give out each year or the type of skills and qualifications that someone might need to have.
Economic migrants will often arrive by aeroplane, but refugees, asylum seekers and illegal immigrants might all try to find the easiest way to cross a border.
From 2015 to the present, a huge number of illegal migrants have journeyed across the Mediterranean Sea to get to Greece, Turkey, Italy or Spain.
Many of these people might already have made their way across deserts or mountain ranges to escape persecution, conflict or war.
These physical barriers can be difficult to cross and many people are intercepted and returned to their place of origin.