First trying to examine the hole with a flashlight from above Gómez could see only darkness, so tied with a line of heavy rope around his waist he was lowered by several colleagues, and descending into the murk he realized it was a perfectly cylindrical shaft. At the bottom he came to rest in apparently ancient construction – a man-made tunnel, blocked in both directions by immense stones. Gómez was aware that archaeologists had previously discovered a narrow tunnel underneath the Pyramid of the Sun, and supposed he was now observing a kind of similar mirror tunnel, leading to a subterranean chamber beneath Temple of the Feathered Serpent. He decided initially to elaborate a clear hypothesis and to obtain approval. Meanwhile, he erected a tent over the sinkhole to preserve it from the hundreds of thousands of tourists who visit Teotihuacán. Researchers reported that the tunnel was believed to have been sealed in 200 CE.