As already indicated, our knowledge of Han pottery is mainly derived from the articles disinterred from the tombs of the period, and this will explain the curious fact that Han pottery was almost unknown until quite recent times, and that information on the subject in Chinese ceramic literature is of the most meagre and least satisfying description. The ancestor-worshipping Chinese have always been averse to the systematic exploration of graves. Whatever their practice may have been when the opportunity occurred of rifling a grave unobserved, this at any rate has been the avowed principle. The result is that though China must be honeycombed with graves and tombs, they have not been overtly disturbed in any numbers until recent years, when extensive railway cuttings have opened up the ground. To the progress of railway engineering the sudden appearance of considerable quantities of mortuary pottery is chiefly due. On the other hand, one of our most interesting finds was made away from the railway in Szechuan. Here, in the neighbourhood of Ch´êng-tu and along the banks of the Min, the soft sandstone hills which line the river had in ancient times been extensively tunnelled with elaborate chambers protected by small entrance doors. Whether these were ever used as dwellings is uncertain, but they certainly became eventually the tenements of the dead. The deposits of ages have covered over the entrances to these tombs, but from time to time torrential rain or some other cause exposed their approaches to the country folk, who invariably pillaged them for coins and smashed and scattered their less marketable contents. The Rev. Thomas Torrance, when stationed at Ch´êng-tu, had the opportunity of exploring some of these caverns, and even succeeded in discovering some unrifled tombs, part of the contents of which he brought over and presented to the British Museum. The funeral furniture of these tombs varied according to the wealth and status of the owner. In the poor man's tomb were unprotected skeletons, small images in a niche, an iron cooking pot, and a few coins. In the rich man's were terra cotta coffins, encased in ornamented slabs, images apparently of the members of his household, a quantity of crockery, and a perfect menagerie of domestic animals and birds. To quote Mr. Torrance's own words:[23] "Standing with your reflector in the midst of a large cave, it seems verily an imitation Noah's Ark."