Since 1990 more than a million people have travelled between Burkina Faso and Côte d'Ivoire, making it Africa's busiest migrant route, according to the World Bank.
Many of the estimated 2.1m expatriates living in the two countries, according to 2010 World Bank figures, travelled along a 1,228km stretch of mostly smooth road that connects Burkina Faso's capital, Ouagadougou, with Côte d'Ivoire's commerical capital, Abidjan. Movement along this African artery is spartan compared to the world's most travelled migrant highway, between Mexico and the United States. About 11.6m Mexican immigrants lived in the US in 2010, according to the bank.
This type of upward migration - to a country with a steep increase in average income - is known as "South-North" migration. It is the most common type of relocation and accounted for 45% of the world's migrant movements in 2010, according to a 2013 report by International Organisation for Migration (IOM).
The Burkina Faso-Côte d'Ivoire corridor, however, is an example of lateral migration. This "South-South" migration involves travelling between poor countries without vast differences in average incomes.
It is the second-most common type of migration, accounting for 35% of migration worldwide, according to the IOM. "North-North" migration - from one high-income country to another (e.g. Germany to the US) - was 17%, and "North-South" was 3%. South-South migration occurs most often at an intra-regional level.
About 1.3m Burkinabe, or about 8% of Burkina Faso's 15.5m population, live in Côte d'Ivoire, according to 2010 World Bank figures. (The UN counted 1.5m in 2013.) They made up about 7% of Côte d'Ivoire's 2010 population of 19m.
Migration in the opposite direction has also been significant. About 840,000 Ivorians live in Burkina Faso, according to the bank.
Like other South-South migration data, these figures are likely to be far higher than reported, according to the IOM, because of the high levels of informal movement and the difficulty of gathering statistics in the developing world.
Burkina Faso is a "low-income" country, with a per capita average income below $1,035, according to the World Bank. Côte d'Ivoire is ranked as a "lower-middle income" country, with expected average income between $1,036 and $4,085 a year. By this measurement, the difference in income does not promise Burkinabes much higher earnings or a better life in Côte d'Ivoire.
So why then have more than 1m people travelled along this route?
In pre-colonial times, the whole of west Africa was one economic unit, according to Aderanti Adepoju, co-ordinator of the Network of Migration Research on Africa, a Nigeria-based academic organisation that focuses on west African migration. People, goods and services flowed freely throughout the region, according to Mr Adepoju. When people migrated they did so mainly in search of security and fertile land.
Colonial economic structures, territorial boundaries and faster transport networks, however, have altered the motivations of migrants as well as their destinations, Mr Adepoju said.
These have led to institutionalised, large-scale seasonal and cross-border labour movements motivated by economic gain. Many Burkinabe travel along the Burkina Faso-Côte d'Ivoire corridor to earn money on Côte d'Ivoire's cocoa and coffee plantations, either travelling seasonally or staying in the country for a few years at a time.
Three factors make migration along this route popular, Mr Adepoju said in a telephone interview with Africa in Fact. The first is income disparity.
Although the differences in expected earnings in the two countries are slim, "Burkinabe can expect to earn more money when they move to Côte d'Ivoire for work", he said.
The second factor is a disparity in resources. Côte d'Ivoire's land is more fertile and provides more opportunities for migrant farmers.
The third factor is the "shared colonial administration between the two neighbouring nations", Mr Adepoju said. "The French colonisation of Burkina Faso and Côte d'Ivoire led to a shared language and currency," he explained. Although both countries are now independent, the French left behind a cultural and economic system that "made it much easier and more attractive for Burkinabe to travel to and from Côte d'Ivoire".
Burkina Faso depends significantly on remittances from its citizens in neighbouring countries to support its economy, wrote Yiriyibin Bambio in a 2011 World Bank book entitled "Remittance Markets in Africa".
Remittances support one-third of Burkina Faso households, according to Mr Bambio. In 2011 77% of these remittances came from Côte d'Ivoire. This proportion increased to 78% in 2012 when Burkinabe sent home $130m in remittances, including $102m from Côte d'Ivoire, according to the World Bank.
The historical relationship between Côte d'Ivoire and Burkina Faso has also had a major influence on this migratory route. In 1963 Côte d'Ivoire's first president, Félix Houphouët-Boigny, issued a decree which gave Ivorian land to those who cultivated it, according to Dwayne Woods, associate professor of political science at Purdue University, in a 2003 article in the Journal of Modern African Studies. In response, Ivorians as well as immigrants from neighbouring countries began farming coffee and cocoa across the country, making Côte d'Ivoire the world's leading cocoa producer.
However, world commodity prices hit a slump in 1990 and cocoa prices plummeted. Three years later Mr Houphouët-Boigny died. Soon after, bitter feuds erupted between Ivorians of different ethnic groups for control of the country and its commodities, and about the rights of foreign workers.
Henri Konan Bédié, who succeeded Mr Houphouët-Boigny, did not share his predecessor's view of land ownership and cultural diversity, according to a 2013 US-AID country profile.
He blamed foreigners for the country's economic woes and instituted the Rural Land Act of 1998, which limited land ownership to the state, public organisations and Ivorian citizens. With the cocoa and coffee industries depressed, Ivorians regarded foreign labour as a threat to their livelihoods. Burkinabe migrants now found it almost impossible to earn a meaningful income from Ivorian land, according to Mr Woods.
Then in December 1999 the military staged a coup and overthrew Mr Bédié, who was replaced in an election by the equally xenophobic Laurent Gbagbo.
By 2002 tensions between Ivorians had reached breaking point. After a failed coup by disaffected soldiers, Côte d'Ivoire degenerated into a civil war that lasted five years and displaced about 700,000 people, according to the World Bank.
Of those displaced, about 400,000 were Burkinabe, wrote sociologist Werner Heuler-Neuhaus in 2011 in Rural21, a development journal.
West Africa, with 8.4m migrants in 2009, has the continent's largest migrant stock and sub-Saharan Africa's largest share of intra-regional migration flows, according to the IOM.
The Economic Community of West African States (ECOWAS) has made much of this movement easier: since 2005 west Africans who hold ECOWAS passports can travel freely for 90 days without a visa through the 15-country ECOWAS zone.
Customs officials still routinely demand bribes from those carrying ECOWAS passports and arrest those who do not comply, according to Adebusuyi Adeniran, a sociology lecturer at Obafemi Awolowo University in Nigeria, in a January 2012 commentary on Africa Portal, an online site.
South-South migrants in west Africa are exposed to conflict, xenophobia, exploitation and the ever-present risk of expulsion from their host countries--all without the guarantee of a better life. Generations of Burkinabe have faced these hardships. Their continued movement indicates that the risks are worth taking.