Seal (Lat. sigillum), a piece of metal, stone, or other hard substance on which is engraved some image or device, and sometimes a legend or inscription. It is used for making impressions on wax or like material affixed to legal instruments, as evidence of their authenticity. The word seal sometimes means only the implement employed, but both in legal and in common language it is applied also to the thing impressed. The Bible contains frequent allusions to seals, and they abound among Assyrian and Babylonian remains. From the East the use of seals passed to Greece and thence to Rome; and it has been common in all the European states from the earliest periods. Among both the Greeks and the Romans the seal was usually set in a ring, whence annulus came to be a Latin name for a seal. The word bulla has always been used in Europe to designate specifically an impression in metal, and thus came to be the distinctive appellation of a class of instruments sealed in that way. Such, for example, are the edicts and briefs of the Roman pontiffs (see Bull, Papal), and some constitutions of the German emperors. - The circular form is common to all periods.

The ogive, the spade form of the escutcheon in heraldry, appeared with the pointed style in architecture, and in the course of time was exclusively appropriated by abbeys, chapters, bishops, and other ecclesiastical bodies and persons. The oval form was particularly frequent in France during the reigns of the Merovingian and Carlovingian kings. The size varied at different periods, and in general the smaller and thicker the seal, the older it is. Those of the Merovingian kings are hardly more than an inch in diameter, while that of Francis I. of France had a breadth of four inches. The Egyptian priests used in sealing a sort of clay. The Byzantine emperors sealed in the form of bulloe with lead, and sometimes with silver and gold. Silver bulloe are much rarer than those of gold. The wax most anciently employed was white. When, about the 9th or 10th century, wax was made of various colors, only emperors and kings might seal in red. In the 12th century it was customary in France to seal with green wax letters addressed to persons of high eminence. This color was introduced into Germany in the 14th century, and was appropriated by religious houses and cities. Blue seals are very rare, and Charles V. of Germany is said to be the only European monarch who used this color.

The patriarchs of Jerusalem and Constantinople, and the grand masters of the order of Malta and of the Teutonic order in Germany, sealed in black. Private persons commonly used yellow wax, and this color is frequent in public documents of about the 12th century. - The devices upon seals throw not a little light upon the manners and usages of different ages, and some of them have positive historical value. The seals of the Romans were engraved with the portraits of their ancestors or friends, with mythological subjects, or with symbolical allusions to the real or mythical history of their families. Perhaps the earliest authentic instance of a seal bearing armorial devices is that of Ar-nulphus, count of Flanders (941). Such seals were not common until the 13th century. The early seals of religious communities and of cities were inscribed with the image of their patron saint or of some sacred relic, or with the figures of ecclesiastical dignitaries or magistrates. The name of the owner in seals attached to public documents usually forms part of the inscription. The ancient intaglios were frequently used for seals in the times of the early French kings.

They were used chiefly for counter-seals, and by the addition of a pious text or legend it was attempted to give a sacred character to their profane subjects. The most ancient mode of sealing was probably that of applying the wax directly to the parchment. When the instrument was written upon two or more leaves, the wax was made to reach them all by impressing it upon an incision made in the parchment in the form of a cross. The seal was sometimes also made upon the ends of thongs or strips of parchment run through the several sheets. Lead, silver, or gold bulloe were almost of necessity appended by a cord or strip. In the 12th century it seems that in France at least pendent seals had displaced the other sort. They are still used generally for letters patent, treaties, and other important public documents. During the 12th century, too, though the practice was not well established until the 13th, arose the contrivance of counter-seals, that is to say, the use of a different impression upon the reverse of the proper seal. They are said to have been first applied to the pendent seals.

They were in these cases made of the same size with the chief seals, and the mottoes interrupted on these were continued on the counter-seals. - Although in some periods seals have taken the place of signatures, yet very often seal and signature have been employed together. In Rome, the praetorian law had recognized the validity of testaments that were only sealed by the witnesses; yet an imperial constitution afterward required the adscription of their names also. In the constitutions of the Merovingian and Carlovingian kings, the seal ordinarily supports the monogram or signature of the sovereign, but sometimes it stands alone. From the 8th to the 10th century the use of seals in France was confined almost entirely to the kings. Most instruments of this period are attested, so far as the witnesses at least are concerned, only by the mention of their names. About the 12th or 13th century the use of seals among all classes became general, and continued so until the revival of learning and the diffusion of correct writing rendered seals of less use. In England charters and grants of the Anglo-Saxon and Anglo-Danish reigns were authenticated by the signature of the grantor preceded by the figure of a cross.

The execution was attested by the subscription of the names of the witnesses, each name being preceded by a cross. Seals were certainly not often used in England until late in the 11th century, and then by no means commonly. There are extant unquestioned seals of Edward the Confessor, and he certainly first adopted a great seal for England; but their general use for authenticating charters and other instruments was not fairly established till near the middle of the 13th century. In Scotland, a statute of the time of Robert III. (1390-1406) declared that every baron or tenant in capite of the king must have a peculiar seal for his sovereign's service; and a statute apparently in aid of this one, passed in the next reign (James I.), enacts that every freeholder shall appear at the lord's court with his seals, or if he cannot appear in person, he shall send them by his attorney; and it seems to have been customary for gentlemen at this time to deposit copies of their seals in the office of the court of their county, the seal then sufficing without signature to authenticate an instrument.

In 1540 a statute of James V. declared that, inasmuch as seals might be lost or counterfeited, all documents must henceforth be not only sealed but subscribed. - From the universal use of seals in England it came to be English law that no charter, grant, or other instrument of conveyance was factum, that is, done, or in other phrase a deed, until it was sealed; and such was the virtue of a seal that down to the time of Charles II. it alone sufficed to make a writing valid and binding. The statute 29 Charles II., the so-called statute of frauds, enacted that certain writings should for the future be signed; but it is probably the better opinion that, even since the statute, a deed duly sealed is good without the subscription of a name. - The old common law definition of a seal is that given by Lord Coke: Sigillum est cera impressa - "A seal is an impression in wax;" but it has long been held that a wafer or other tenacious substance, on which an impression is or may be made, is a good seal. In many, perhaps indeed most of the United States, neither wax, wafer, nor any other substance is required; a scroll or ring made with the pen in imitation of the seal, or as marking its place, being sufficient.

One piece of wax suffices for several signers if stamped with their separate impressions, or several signers may adopt one seal; and an adoption of this sort is inferred when the deed recites the sealing "with our seals," and those who did not in fact seal do yet sign and deliver the deed. The significance of the seal in law at present is, that it imports a deliberate and considered act on the part of him who affixes it. The rule has established itself firmly in the law, that an instrument thus executed with a seal implies a consideration, or in other words that full assent which is essential to the validity of every contract, and which can be inferred only from a seal, or from something of value passing between the parties as the cause of the contract.