You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Kenya

Context:
The African Great Lakes region, which Kenya is a part of, has been inhabited by humans since the Lower Paleolithic period. By the first millennium AD, the Bantu expansion had reached the area from West-Central Africa. The borders of the modern state consequently comprise the crossroads of the Niger-Congo, Nilo-Saharan and Afroasiatic areas of the continent, representing most major ethnolinguistic groups found in Africa. Bantu and Nilotic populations together constitute around 97% of the nation's residents. European and Arab presence in coastal Mombasa dates to the Early Modern period; European exploration of the interior began in the 19th century. The British Empire established the East Africa Protectorate in 1895, which starting in 1920 gave way to the Kenya Colony. Kenya obtained independence in December 1963. Following a referendum in August 2010 and adoption of a new constitution, Kenya is now divided into 47 semi-autonomous counties, governed by elected governors.

Question:
When did the exploration of the interior begin?

19th century