During our annual travels, 8 Vermillionaires placed the cache in a cairn on the line of rocks demarcating the Tropic of Capricorn, about 21 steps from the sign on the west.
Appropriately enough cairns were associated in Greek mythology with Hermes - the god, among other things, of travelers and of boundaries. The tropic itself is not static but is moving northward, currently at a rate of 15 meters per year. When the tropic was named the sun was in Capricorn at the December solstice. (Today the sun would be in Sagittarius.)
The cache contains some mementos from our travels and a Trackable. Heading eastwards from the Prime Meridian, the Tropic of Capricorn passed through 10 countries: Namibia, Botswana, South Africa, Mozambique, Madagascar, Australia, Chile, Argentina, Paraguay and Brazil. As Hermes was said to convey travelers, please convey the Trackable to the other 9 countries crossed by the tropic.