Spider
A triangulation point, or trig point, consists of a concrete or stone pillar, typically around 1.2 meters high, with a brass plate on top. This plate, often called a "spider," has three arms and a central depression for mounting a surveying instrument like a theodolite. There should be a plug in the middle, to prevent ingress of dirt and water that could interfere with the theodolite - this one is missing (probably taken as a souvenir).
Spider
A triangulation point, or trig point, consists of a concrete or stone pillar, typically around 1.2 meters high, with a brass plate on top. This plate, often called a "spider," has three arms and a central depression for mounting a surveying instrument like a theodolite. There should be a plug in the middle, to prevent ingress of dirt and water that could interfere with the theodolite - this one is missing (probably taken as a souvenir).