'And now to investigate the secrets of the ruined city wherein dwelled Tsin the mighty, Tsin, the ruler of a tiny principality, who years and years ago set himself one of the biggest tasks man has ever undertaken.'

They were seated in their tent in the light shed by a candle lamp, and the Professor lolled back on the tiny camp-bed which was to be his own special property. Indeed, a glance round the camp showed clearly that the expedition was organised thoroughly, and promised by the equipment it carried to give comfort to every one. For first, there was the large tent for the use of the Professor, David, and Dick, with its three narrow beds, its collapsible table and chairs, and its waterproof flooring. Then, a little distance away was a smaller, bell tent, in which Alphonse was to repose, and beside it, within easy reach, a field kitchen, while further still was a third tent, similar to that occupied by Alphonse, for the accommodation of the four Chinese.

'Of course, those whom we employ to help us with the digging will have to find their own quarters,' said the Professor at the very beginning of their forming camp. 'There happens to be a village some two miles away, and no doubt the inn there will take them in. But there are also one or two old buildings still standing in this ruined place, and they will probably elect to settle there.'

That, in fact, was what the dozen coolies whom he had hired had decided on. Already they had secured the basement of what had been a two-storied house, though now the upper part had gone, while to effect an entrance into that below needed quite a lot of excavation. For the rest, the camp was pitched on a grassy knoll some hundred yards from the ruins and within three miles of the huge Chinese wall, which, not so perfect now-a-days as it was wont to be, is still a marvel of human ingenuity and perseverance, stretching as it does for fourteen hundred miles over hill and valley, cutting the northern provinces of China from the rest of the world.

'As I was saying,' began the Professor again, 'we are about to investigate the ruins of the city—quite a small place, I imagine—in which dwelt Tsin, the one-time ruler of a small province in this neighbourhood. You must understand that he was one of many kings controlling the numerous provinces into which China was divided some two thousand years ago, a somewhat different condition to that now ruling, for there are only some fifteen provinces now-a-days. Tsin, like all the rest of these little kings, was for ever squabbling with his neighbours, so that there were frequent little wars, and as a natural consequence many additions were made to, or territory taken from, the various lands belonging to these kings. However, Tsin seems to have been fortunate, for he made additions. In fact, he ate up his neighbours, and with more wealth and more men increased wonderfully in power. He ended by conquering every part of China, and becoming Emperor of the Celestial Empire.'

'And richly deserved his reward, no doubt,' ventured David. 'I should imagine that the people were all the happier for having one ruler only. Trade and other matters must have gone more smoothly.'

'I agree with you; things probably were more fortunate. But Tsin was not without his troubles; his kingdom was for ever being invaded by Mongolian nomads from the north, nomads who were as elusive as they were warlike. They devastated portions of his kingdom, and when armies were sent in pursuit they melted away, taken in ambush, or lost hopelessly in the desert. It was to check those nomads that Tsin started the Great Wall of China beside which we lie, and no doubt, once completed, it fulfilled its purpose. It will repay a visit one of these days.'

Dick and David had, as a matter of fact, already visited the huge wall, and had marvelled at its vastness. For this Great Wall of China is not merely an erection two bricks thick; it is a huge earth wall, faced with masonry, buttressed and supported everywhere, and freely supplied with fortified gates and quarters for its garrison. Fourteen hundred miles of it, stretching across the kingdom! Think of the enormous labour, think of the host required to guard its length. And to-day it is deserted, or almost so. The broad track on its summit, constructed of such a width that three carts could conveniently be driven side by side, is now no longer of service. Mongolia has ceased to send in her nomads. Perhaps the very presence of the wall has prevented them, or maybe they have become less warlike. There the wall lies, a work to rouse the admiration of modern-day people.

'And now to speak of these ruins. They are small, as I have said already,' the Professor told them, 'and since I do not expect to discover much of interest, I have decided to send you two lads forward. John Jong shall go with you, while the naval officer who spoke such excellent English has provided me with passports. It seems that his father is a mandarin, and commands the district a hundred and fifty miles north, where are located the Mongolian ruins I am so anxious to investigate. Will you go?'

Would they go? David and Dick were as eager as the Professor himself to dip into the past by investigating the ruins of the city in which Tsin had dwelled so many hundreds of years before. But a journey through China offered superior attractions; and besides, there was another city to be visited, or rather the ruins of one that had formerly existed.