The most influential single cultural factor in Trinidad and Tobago is Carnival, brought to Trinidad by French settlers from Martinique in the later part of the 18th century. Originally the celebration was confined to the elite, but it was imitated and adapted by their African slaves and, after the abolition of slavery in 1838, the practise spread into the free population. The Canboulay Riots of 1881 were a turning point in the evolution of Trinidad Carnival. Carnival was originally confined to the upper classes, which rode the streets in floats, or watched from the upper stories of residences and businesses. The night was given over to the lower classes. The first few hours of Carnival Monday morning, from about 4 am until sunrise was known as "J'ouvert" (a contraction of "jour ouvert"). Costumed and masked by the darkness, J'ouvert allowed the wealthy to mix with the poor in relative anonymity. Monday night ("night 'mas") had a similar, but lesser function.