At the end of 2004 - early 2005, the Việt Nam Institute of Archaeology in cooperation with the Management Department of Hà Nội Relics and Landscapes conducted an archaeological survey and excavation at Thượng Temple before its reconstruction and found a furnace (for casting three-barbed bronze arrows). This is a new important and valuable discovery as it could serve as evidence for decoding the legendary mystery of the magic crossbows in the King An Dương period. In 2006 and 2007, the Việt Nam Institute of Archaeology and the Center for Conservation of Cổ Loa site – Ancient Citadel (the Centre for Conservation of Thăng Long - Hà Nội Heritage today) continued to excavate at Thượng Temple and discovered a system of remaining bronze-casting furnaces and many secions of stone moulds, etc.

The collection of Cổ Loa bronze-casting moulds was discovered at the same time as the remaining furnaces of which there is a clear structure of a pipe for leading wind into the furnace with dense ash of burning fuel around the furnace, broken and intact sections of moulds, draft moulds, discarded products and waste together with stone materials and the products such as bronze arrows, broken pieces of crucibles, bronze slags. They were archaeologically dated to the Cổ Loa period (equivalent to the period of the Đông Sơn Culture - early Iron Age), the third - second centuries BC, equivalent to the King An Dương period -  Âu Lạc state. The Collection of Cổ Loa moulds include three-sectioned and two-sectioned moulds, with 11 artifacts, 10 of which are the moulds for casting three-barbed bronze arrows and one for casting bronze arrows with swallow wing-shaped heads. They are dated to  the Đông Sơn culture - early Iron Age, the third and second centuries BC. These are original, unique artifacts that have been known in Việt Nam to date. Moreover, this discovery also serves as convincing evidence for the indigenousness of the products which are called by a respected proper name: Cổ Loa bronze Arrows.

In 2020, the Center for Conservation of Thăng Long - Hà Nội Heritage sorted out the typical moulds for casting bronze arrows and javelins (the Collection of Cổ Loa moulds) to set up a dossier for recognition as a National Treasure. On December 31, 2020, the Collection of Cổ Loa moulds was recognized as a national treasure (Phase 9) by the Prime Minister’s Decision No. 2283/QĐ-TTg.

The Thượng Temple – the Temple for worshipping King An Dương - is located at the southwest corner of the Innermost Rampart (Legend has it that it used to be a royal palace) where many traces of bronze-casting furnaces were discovered, serving as a metallurgical centre of Cổ Loa Imperial city in King An Dương period. The casting of the Cổ Loa bronze arrows was a military secret, carefully controlled by the Âu Lạc state.

Outline of the three ramparts of the Cổ Loa citadel and the location where the collection of the stone mould sections were found

Position where bronze-casting furnace traces were found

The bronze-casting furnaces were located in the Inner Rampart in the area behind the Royal Harem, of the Thượng Temple, which was found from the cultural layer of Cổ Loa period, from the third – second centuries BC. Their function was metallurgy and bronze casting, mainly for casting three-barbed arrows.

Traces of the bronze-casting furnace system were found in the excavation in 2007

Traces of the bronze-casting furnace in the excavation in 2006

Plane where the traces of the bronze-casting furnace system were found in the excavation in 2007

Mould sections, ruined moulds, stone material and copper slags in the bronze-casting furnace in the excavation in 2006

Copper slag and broken crucible found in 2005

Clusters of mould sections, draft moulds, and waste from a furnace found in 2006

Javelin-casting mould found in 2006 (three-sectioned mould)

Professor Trần Quốc Vượng and scientists are looking at the artifacts displayed at the Conference for preliminary reports on the results of the excavation at Thượng Temple in 2005

Conference for preliminary reports on the results of the excavation at Thượng Temple in 2005

Former State President Trần Đức Lương is visiting the excavation site of the bronze-casting furnace in 2007

MANAGEMENT DEPARTMENT OF COLOA VESTIGE SITE