Laudator Temporis Acti

Horace, Odes 1.32.13-14:

O decus Phoebi et dapibus supremi
  grata testudo Iovis!

O glory of Phoebus, turtle welcome even at the feasts of highest Jove!

When I read these lines I sometimes imagine that Horace is talking about turtle soup, which of course he's not. But I'm not the only one who has made this connection. Thackeray in his Burlesques writes:

'Twas noon in Chepe. The ware-rooms were thronged. The flaunting windows of the mercers attracted many a purchaser: the glittering panes behind which Birmingham had glazed its simulated silver, induced rustics to pause: although only noon, the savory odors of the Cook Shops tempted the over hungry citizen to the bun of Bath, or to the fragrant potage that mocks the turtle's flavor--the turtle! O dapibus supremi grata testudo Jovis! I am an Alderman when I think of thee! Well: it was noon in Chepe.

It was thought that London alderman were especially fond of turtle soup and dined on it at their banquets. The Oxford English Dictionary defines turtledom as "a collective name for those who eat turtle (i.e. spec. London aldermen)." Thackeray's circumlocution "the fragrant potage that mocks the turtle's flavor" refers to mock turtle soup, actually made from the head of a calf.

Horace was thinking not of turtle soup, but of the lyre, invented by Hermes and first made from the shell of a tortoise (Latin testudo, Greek chelys). The Homeric Hymn to Hermes (22-56, tr. Hugh G. Evelyn-White) tells the story:

But as he stepped over the threshold of the high-roofed cave, he found a tortoise there and gained endless delight. For it was Hermes who first made the tortoise a singer. The creature fell in his way at the courtyard gate, where it was feeding on the rich grass before the dwelling, waddling along. When he saw it, the luck-bringing son of Zeus [Hermes] laughed and said:

"An omen of great luck for me so soon! I do not slight it. Hail, comrade of the feast, lovely in shape, sounding at the dance! With joy I meet you! Where got you that rich gaud for covering, that spangled shell --a tortoise living in the mountains? But I will take and carry you within: you shall help me and I will do you no disgrace, though first of all you must profit me. It is better to be at home: harm may come out of doors. Living, you shall be a spell against mischievous witchcraft; but if you die, then you shall make sweetest song."

Thus speaking, he took up the tortoise in both hands and went back into the house carrying his charming toy. Then he cut off its limbs and scooped out the marrow of the mountain-tortoise with a scoop of grey iron. As a swift thought darts through the heart of a man when thronging cares haunt him, or as bright glances flash from the eye, so glorious Hermes planned both thought and deed at once. He cut stalks of reed to measure and fixed them, fastening their ends across the back and through the shell of the tortoise, and then stretched ox hide all over it by his skill. Also he put in the horns and fitted a cross-piece upon the two of them, and stretched seven strings of sheep-gut. But when he had made it he proved each string in turn with the key, as he held the lovely thing. At the touch of his hand it sounded marvelously; and, as he tried it, the god sang sweet random snatches, even as youths bandy taunts at festivals.

Testudo has another unusual meaning in Latin. Roman soldiers sometimes held their shields flat over their heads, in such a way that the shields overlapped, to protect themselves from enemy missiles. This formation was known as a testudo, a tortoise. Dio Cassius 49.30 (tr. E. Cary) has a good description of the military testudo:

This testudo and the way in which it is formed are as follows. The baggage animals, the light-armed troops, and the cavalry are placed in the centre of the army. The heavy-armed troops who use the oblong, curved, and cylindrical shields are drawn up around the outside, making a rectangular figure; and, facing outward and holding their arms at the ready, they enclose the rest. The others, who have flat shields, form a compact body in the centre and raise their shields over the heads of all the others, so that nothing but shields can be seen in every part of the phalanx alike and all the men by the density of the formation are under shelter from missiles. Indeed, it is so marvellously strong that men can walk upon it, and whenever they come to a narrow ravine, even horses and vehicles can be driven over it. Such is the plan of this formation, and for this reason it has received the name testudo, with reference both to its strength and to the excellent shelter it affords. They use it in two ways: either they approach some fort to assault it, often even enabling men to scale the very walls, or sometimes, when they are surrounded by archers, they all crouch together — even the horses being taught to kneel or lie down — and thereby cause the foe to think that they are exhausted; then, when the enemy draws near, they suddenly rise and throw them into consternation.