The Voortrekkers were a group of about 15.000 Dutch-descended Afrikaners who emigrated inland from South Africa's coastal colonies, which were controlled by the British, from about 1835 to 1855. They overcame great natural obstacles (rivers, mountains, etc.) in their ox-wagons and fought battles against many of the black tribes inland. To commemorate their exploits, a reenactment of their trek took place in 1938, at the centennial of the original event. In addition, a big monument was built near the executive capital of South Africa, Pretoria. A huge marble frieze runs along the inside walls of the monument and depicts some of the Voortrekkers' challenges and exploits (purely from a white Afrikaner perspective, of course). In the dome-shaped ceiling, there is a small hole; on the 16th of December each year, the sun shines through the hole onto a marble slab in the basement which bears the inscription "Ons vir jou Suid-Afrika" (We for thee South Africa). The 16th of December was the date on which a small group of Afrikaners fought off an attack by a numerically far superior force of Zulus without suffering any losses. The date was and is a public holiday -- originally the Day of Blood River, then the Day of the Vow, now the Day of Reconciliation.