His pupil, Shaba, was the first civilized man to circumnavigate Lake Ushindi. He discovered that the Cartius, as was known, enters Lake Ushindi, but that only two rivers flow out of Ushindi, the Kamba and Nyoka. The actual source of the tributary to the Vosk, now called the Thassa Cartius, as you know, was found five years later by the. explorer, Ramus of Tabor, who, with a small expedition, over a period of nine months, fought and bartered his way through the river tribes, beyond the six cataracts, to the Ven highlands. The Thassa Cartius, with its own tributaries, drains the highlands and the descending plains."

"That has been known to me for over a year," I said. "Why do you speak of it now?"

"We are ignorant of so many things," mused Samos.

I shrugged. Much of Gor was terra incognita. Few knew well the lands on the east of the Voltai and Thentis ranges, for example, or what lay west of the farther islands, near Cos and Tyros. It was more irritating, of course, to realize that even considerable areas of territory above Schendi, south of the Vosk, and west of Ar, were unknown. "There was good reason to speculate that the Cartius entered the Vosk, by way of Lake Ushindi," I said.

"I know," said Samos, "tradition, and the directions and flow of the rivers. Who would have understood, of the cities, that they were not the same?"

"Even the bargemen of the Cartius proper, the subequatorial Cartius, and those of the Thassa Cartius, far to the north, thought the rivers to be but one waterway."

"Yes," said Samos. "And until the calculations of Ramani, and the expeditions of Shaba and Ramus, who had reason to believe otherwise?"

"The rain forests closed the Cartius proper for most civilized persons from the south," I said, "and what trading took place tended to be confined to the ubarates of the southern shore of Lake Ushindi. It was convenient then, for trading purposes, to make use of either the Kamba or the Nyoka to reach Thassa."