The seal thus contains motifs that visually identify the sovereign or state signatories. It functions as a visual certificate of authority beyond the written words of the treaty. Its inclusion broadens the symbolic dimension of the seal by appealing to universal values or to a shared political ideal. The use of the seal to conclude treaties visually inscribes their signature within a shared political space or within an international tradition.

The seal’s visual strength lies precisely in its ability to incorporate elements that attest to state power legitimised by image as much as by legal text, thereby conferring upon diplomatic instruments an immediate visual authority within the diplomatic context.

The location where the originals of the European treaties are kept is far from a trivial detail: it reveals the very nature of the Union. The EU treaties remain international treaties, over which the Member States retain control within their sovereign powers as recognised in international law. This explains why the originals are held by State repositaries rather than by the Union itself. Thus, in 1957, when the Treaties of Rome were signed, the host State – in this case Italy – became the depositary of the treaties. This is why the originals of the European treaties following the Treaties of Rome, as amendments thereto, were in turn entrusted to the archives of the Italian Ministry of Foreign Affairs, at the Farnesina. The Historical Archives of the European Union preserve memory and sources, but not constitutive authority. This choice reflects the fundamental tension of the EU: an autonomous legal order in its operation, yet one that remains intergovernmental in its foundations. It is therefore a matter of courtesy on the part of the Member States that the HAEU were provided with certified true copies of the Treaties of Rome (cf. juxta), as well as facsimiles of the Treaty of Maastricht (cf. juxta) and of the Treaty of Accession 2003 (cf. infra).

In its politico-legal dimension, the seal validates the authenticity of documents issued by the various European institutions. Certain collections of original official documents thus turn out to be authenticated and certified copies, precisely by virtue of the seal of the Registry affixed to them. The Council of the European Economic Community (EEC) provided the European Parliament with copies of the various concluded Official Acts, authenticating them by affixing the seal of the Secretary-General of the Council of the EEC.

Similarly, the Special Council of Ministers of the ECSC performed simultaneously the same function, as an authority empowered to issue certified true copies bearing its seal, notably of the minutes recording the appointment of the members of the Consultative Committee.